The Archaeotectural Exploration of the 13th Century Terraced Building F1 at the Laogulou Yashu Archaeological Site in Chongqing, China

Abstract

The Laogulou Yashu Archaeological Site in Chongqing represented a significant discovery in the study of medieval Chinese urban heritage. Among its remains, the 13th century terraced building F1 stood out for its scale and function as a governmental qiaolou (gate tower). This study reconstructed the original architectural design of F1 using an archaeotectural approach that integrated archaeological evidence and Song Dynasty architectural treatises, especially Yingzao Fashi, and comparatively analysed the building with contemporaneous structures and visual references. By applying the statistical estimation of historical measurement units (chi), typological analysis based on modular standards (cai) and the interpretive modelling of structural elements, the research offered a historically grounded and dimensionally coherent reconstruction. The study not only enhanced the understanding of Southern Song governmental architecture but also contributed a replicable methodological framework for reconstructing complex historical buildings from fragmentary archaeological data.

1. Introduction

The Laogulou Yashu Archaeological Site is located at the centre of Chongqing, at the mid-level of the southern Yuzhong Peninsula, facing the Yangtze River. The site has a generally rectangular layout, crossed by the east–west Jiefang East Road and north–south Baxian Yamen Street at its centre (Figure 1). The site was first discovered during an urban renewal project in late 2009, having been used as the office site of the local prefectural and county governments since the 10th century. The site contains, reputedly, the highest-hierarchy and largest-scale yashu (衙署, governmental office) remains in the area. Considerable remains from multiple eras have been discovered at the site, among which the terraced building F1 was the most significant. The footprint of F1 covers a considerable area on both the north and south side of the current Jiefang East Road, indicating the huge scale of the building.

According to local chronicles, the yashu of the Chongqing Prefecture (府, Fu) was constructed axially east–west inside the Taiping Gate in the Jiatai Era of the Southern Song Dynasty (1201–1204). In the Chunyou Era (1241–1252), the governor of Sichuan Province (四川制置使, Sichuan Zhizhishi) and the Chongqing Prefecture (重庆知府, Chongqing Zhifu), Yu Jie (余玠) moved his base to Chongqing and renovated the yashu, making this site the centre of the region [1]. This record is in accordance with the datemark of 1245 on the bricks at the Laogulou Yashu Archaeological Site, and we can infer that F1 was the qiaolou (谯楼, a building in the yashu used to store drums and horns for time signals and salutes) of the prefectural yashu [2]. Since then, F1 has undergone reconstructions, renovations and changes in function, and the traces of this have been found in archaeological discoveries. Nevertheless, no specific building records or construction archives about this building from this era of socio-political upheaval have been preserved or discovered.

In the 1360s, F1 was used as the main entrance of the Great Xia regime’s palace, and it was destroyed during the fall of the regime in 1371 [3]. The qiaolou was consequently reconstructed in the Ming Dynasty and a clepsydra was installed inside the building. As drums were used as a time signal in ancient China, the building was commonly named the gulou (鼓楼, literally drum tower), which defined the toponym of this area. In the early 18th century, the gulou was rebuilt again around one century after being destroyed during the civil war. Around half a century later, the axis of yashu shifted to the north–south direction, meaning that there are currently two crossing axes on the archaeological site. In the modern era, the area developed as the financial centre of the city as it was the location of customs administration for foreign companies. In 1927, the gulou was completely demolished during the widening of Lin Sen Road (current Jiefang East Road), and a women’s prison was built on the site in a later period [4]. After being discovered, the site was evaluated as one of the annual top ten archaeological discoveries of China in 2012 and was listed as a Major Historical and Cultural Site Protected at the National Level in 2013.

This study employed an integrated archaeotectural methodology to reconstruct the original design of F1 at the Laogulou Yashu Archaeological Site. Primary data was systematically collected through archaeological excavations undertaken between 2010 and 2022. These data were obtained through manual measurements, stratigraphic documentation and the spatial mapping of structural remains, including postholes and brickwork. To interpret the dimensional logic and construction norms of the period, the research drew upon the Yingzao Fashi (营造法式, also transliterated as Ying-tsao fa-shih, literally Treatise on Architectural Methods or State Building Standards, abbreviated as Fashi hereafter) [5,6]. This Song Dynasty architectural manual compiled the codified design standards employed by imperial construction offices. Statistical analysis was conducted to estimate the historical unit of measurement (chi, 尺), following established methods from prior research on similar sites in Chongqing [7]. Furthermore, comparative analysis of contemporaneous architectural works and iconography, such as Along the River During the Qingming Festival, were used to infer design components that were not directly preserved in the archaeological record [8,9,10,11]. Throughout the process, the methodology carefully acknowledged the limitations imposed by the fragmentary nature of the remains and explicitly distinguished between empirical evidence and interpretive reconstructions.

In recent years, there has been growing scholarly interest in reconstructing historical architecture from partial remains, particularly in East Asia. Nevertheless, several critical gaps remained. Although digital restoration projects have advanced the visualisation of lost structures [12,13], they often depend heavily on fragmentary evidence and seldom formalise the inferential reasoning process linking archaeological clues to architectural hypotheses. Similar efforts, such as the reconstruction of 17th- to 8th-century BCE timber buildings, focused on digital output but rarely addressed the uncertainties inherent in reasoning from incomplete remains [14]. Additionally, discourses on authenticity and ‘destructive reconstruction’ in Chinese heritage practices tend to foreground ideological and policy concerns rather than epistemological methods [15]. The ritualised reconstructions of sacred architecture in Japan further highlight cultural continuity but do not offer methodological frameworks for deducing lost architectural forms [16]. Lastly, studies on ruin interpretation emphasise memory and meaning but seldom address the formal mechanisms by which architects infer original designs [17].

This body of scholarship highlighted a conspicuous methodological gap in archaeotectural research: the absence of systematic, quantifiable reasoning models that could be applicable in East Asian contexts where direct documentation is lacking. This study directly addressed this gap by developing a transparent archaeotectural reasoning framework that incorporated statistical measurement system estimation, typological analysis and structured inferenced from visual and textual sources. It offers a replicable approach for deducing original architectural forms from fragmentary remains, thereby contributing a rigorous and regionally relevant model to the field.

The aim of this research was to reconstruct the original spatial layout and structural logic of F1 through an archaeotectural framework that combined archaeological evidence with historical texts and architectural typology, thereby providing original insights in the absence of direct documentation. The study made a contribution to ongoing scholarly debates about the application of Fashi standards in regional contexts, especially in Southwestern China where few large-scale Southern Song governmental buildings have been documented through archaeological investigation. It addresses a significant gap concerning how imperial design norms were adapted in frontier administrative centres like Chongqing and offers a methodological model for reconstructing complex historical buildings from incomplete data.

2. Material and Methods

2.1. Archaeological Data Collection

After its discovery in 2009, the Laogulou Yashu Archaeological Site underwent two phases of archaeological excavation. The first phase was conducted from 2010 to 2012, discovering 261 remains dating from the 10th century to the modern era with an area of 12,360 square metres on the north side of Jiefang East Road; the second phase involved the excavation of approximately 800 square metres on the south side of Jiefang East Road.

These archaeological works identified the scale and layout of F1, which was a large-scale structure constructed on a rammed earth terrace with brick finishes (Figure 2). The layout of F1 generally follows a U-shaped configuration. There is an altitude drop of four metres from the northwest corner of the terrace’s footprint to its southeast corner. A gateway was located at the centre of the structure, with two guardrooms (门塾, menshu) positioned on either side of the gateway. As postholes were identified on the site (Figure 3), it was inferred that the gateway and guardrooms together formed a structure with seven spans in longitude and five transverse spans. The brick finishing of the rammed earth terrace exhibited both Flemish Bond (one stretcher between headers in each row) and Monk Bond (two stretchers between every header in each row) patterns, whose bricks were carved with the year of construction—‘Year Yisi of Chunyou (淳佑乙巳, 1245)’ (Figure 4) [2].

2.2. Dimensional Analysis and Estimation of Measurement Unit

The base unit of length in ancient China was chi, and it was related to other units of length as follows: one zhang (丈) = 10 chi (尺) = 100 cun (寸) [18]. Various measurement systems were historically employed in building construction, including but not limited to the official system, carpenter system (木工尺, Mugongchi) and Luban system (鲁班尺, Lubanchi, or 文公尺, Wengongchi), in ancient China [19]. According to historical records and measuring rods, the length of one chi in the Song Dynasty varied across different periods and locations but centred around 310 mm [20,21]. Comparative research and archaeological discoveries have indicated that the length of one chi typically ranged between 312 mm and 318 mm [22,23], and some extreme examples of 320 mm have also been discovered [20]. The unit chi of the Fanjiayan Archaeological Site at Diaoyucheng, also locating in Chongqing, was estimated as 318 mm [7]. Hence, the unit length of chi for F1 was estimated to fall within the range of 310 mm to 318 mm according to these data. The possible range of length was conservatively expanded to cover 300 mm to 320 mm to determine the exact length of chi.

The unit length for chi was estimated according to the span lengths by statistical analysis, as halves and whole numbers were commonly used for measurements in historical construction practices. The possibility of each length of chi was evaluated by dividing the measured dimensions at the archaeology site (

Table 1. Dimensions measured on site.

Dimension		Readings (mm)
Interior Structure	Total longitudinal length	39,470
	Total transversal length	14,580
	Central longitudinal span	7170
	Secondary longitudinal spans	6030
	Tertiary longitudinal spans	5900
	Quaternary (end) longitudinal spans	4220
	Central transversal span	5900
	Peripheral (first and third) transversal spans	4340
Gateway	Width	3850
Foundation of Terrace	Top longitudinal length	69,100
	Top transversal length	24,400
	Base longitudinal length	71,480
	Base transversal length	27,190

) by every half chi (Equation (1)). This method enabled the quantitative determination of the most likely length of chi for this research by finding the minimum standard deviation [7].

$$A={\displaystyle \frac{1}{N}}{\sum }_n\left({\displaystyle \frac{\left|\frac{1}{2}\left[\frac{{2L}_i}{x}\right]\times L_i-L_i\right|}{L_i}}\right)$$

(1)

in which $L_i$ represents the dimensions measured at the site, $x$ denotes the possible unit length of chi, and $N$ refers to the number of measured dimensions at the site, totalling 13 in this case. The lower the ratio calculated by the above equation, the easier it becomes to round the measured values to the corresponding unit length.

The results (Figure 5) indicated that the lowest ratio occurred at a unit length of 310 mm, and the corresponding ratio for 311 mm was similarly low. The difference between these values was not sufficiently significant to determine the unit length conclusively. Therefore, the standard deviation of the measured values, calculated based on their deviation from multiples of half-chi, was employed to further assess the possible unit length (Equation (2)).

$$\sigma =\sqrt{{\displaystyle \frac{{\sum }_{i=1-n}{\left(\frac{2L_i}{x}-\left[\frac{2L_i}{x}\right]\right)}^2}{N}}}$$

(2)

in which $L_i$ represents the dimensions measured at the site, $x$ denotes the possible unit length of chi, and $N$ refers to the number of dimensions measured at the site, which was 13 in this case. The results indicated that relatively low values occurred at unit lengths of 301 mm, 310 mm, 311 mm, 317 mm and 320 mm, all of which yielded values below 0.25 (Figure 6). By comprehensively considering these two indicative values, 310 mm was identified as the most reasonable estimate for the unit length of chi.

There were two standardised sizes of bricks stated in Fashi, 12 × 6 × 2 cun and 13 × 6.5 × 2.5 cun, with proportions of $2:1:{\displaystyle \frac{1}{3}}$ and $2:1:{\displaystyle \frac{13}{5}}$, respectively. The bricks discovered at the archaeological site measured approximately 370 × 189 × 95 mm, with a proportion of $2:1:{\displaystyle \frac{1}{2}}$, which did not correspond precisely to either standardised proportion described in Fashi. Nevertheless, the proportion of length and width was $2:1$, consistent with both standardised sizes. According to the bed proportion of the on-site bricks, the brick size was estimated to correspond either to 12 × 6 × 3 cun or to 13 × 6.5 × 3.25 cun.

If the brick was assumed to correspond to the latter size, the derived unit length of chi would have fallen within the range of 285 mm and 292 mm, which was below the generally accepted range for the Song Dynasty and deviated from values identified at comparable sites, such as the 318 mm recorded at the Fanjiayan Archaeological Site in Chongqing. In contrast, the 12 × 6 × 3 cun configuration yielded a unit length ranging from 308 mm to 317 mm, which better aligned with regional standards.

Reverse verification using a unit length of 310 mm produced a theoretical brick size of 372 × 186 × 93 mm, which closely matched the on-site measurements. The small discrepancies, approximately two to three mm per dimension, fell within the expected margin of error for archaeological measurements. Although several unit lengths, including 311 mm and 317 mm, also exhibited low statistical deviation, 310 mm provided the most consistent result across the applied analytical methods. It not only exhibited a low deviation ratio but also corresponded most closely with both the measured brick dimensions and the historically accepted range of chi lengths in Southern Song-era Chongqing. This convergence of evidence reinforced the estimation of 310 mm as the most appropriate unit length in this study.

2.3. Identification of Building Module and Classification

The building module, cai (材, also transliterated as ts’ai), was the most critical standard for building construction, as described in Fashi [24]. There were eight tiers of cai designated, and each tier corresponded to a specific measurement module and was applied according to the hierarchy of buildings [25]. The term cai not only referred to a standard-sized piece of timber, with depth-to-width ratio of 3:2, used for its designated tier, but also served as a unit of length, equivalent to the depth of the standard-sized timber [26]. One fifteenth of a cai was defined as fen (份, also recorded as 分°, literally share), which was the most widely used unit for building design and varied according to the tier of cai applied to the building (Figure 7,

Table 2. Tiers of cai and corresponding application scenarios.

Tier of cai	Length of cai (cun)	Length of fen (cun)	Scenario of Application
1	9	0.6	Diange with 9 to 11 longitudinal spans
2	8.25	0.55	Diange with 5 to 7 longitudinal spans
3	7.5	0.5	Diange with 5 longitudinal spans, double-eaved diange with 3 longitudinal spans, tingtang with 7 longitudinal spans
4	7.2	0.48	Diange with 3 longitudinal spans, tingtang with 5 longitudinal spans
5	6.6	0.44	Small diange with 3 longitudinal spans, large tingtang with 3 longitudinal spans
6	6	0.4	Tingxie (亭榭, pavilion), small tingtang
7	5.25	0.35	Small diange, tingxie, etc.
8	4.5	0.3	Caisson ceiling of diange, small tingxie

) [27]. As the remains of F1 showed seven longitudinal spans, it was likely to have been either a diange (殿阁, a palatial-style hall) employing Tier 2 cai or a tingtang (厅堂, a hall ranked lower than diange) employing Tier 3 cai.

If F1 was identified as a diange employing Tier 2 cai, the diameter of its columns would have been 2.8 cai to 3 cai according to Fashi. Its columns’ diameters were 23.1 cun to 24.75 cun. Based on the previous estimation of the unit length of chi, one cun was 31 mm in the metric system. This indicated that the column diameter would have been between 716.10 mm and 767.25 mm [28], which exceeded the diameter of the postholes at the site, which measured approximately 500 mm. Similarly, if F1 was identified as a tingtang employing Tier 3 cai, the column diameter would have been 2.6 cai, corresponding to 558 mm (18 cun), which was closer to the diameter of the postholes. This suggested a higher likelihood that F1 was a tingtang employing Tier 3 cai.

2.4. Use of Documentary and Visual Sources

In addition to archaeological field data, this study utilised documentary and visual sources to infer architectural design elements that were either fragmentary or absent from the preserved remains on-site. Fashi served as the principal textual source. Its architectural typologies, construction standards, modular systems (cai) and design guidelines for terraces, timber structures and roofing systems were systematically referenced to support dimensional reconstruction and interpret structural logic.

To supplement these textual sources, contemporaneous architectural examples and ancient visual materials were consulted. These included historic paintings and surviving buildings from comparable historical periods. These were selected based on typological and chronological relevance and served to validate inferred features including roof forms, bracket systems, the gateway and decorative components. Where archaeological evidence was insufficient for direct determination, these documentary and visual references were triangulated with excavated measurements to justify interpretive decisions. This integrative multi-source approach facilitated a historically grounded and internally consistent reconstruction of the building’s original form.

3. Results

The individual architectural elements (terrace and timber structure) are analysed in a modular sequence in this section. These components were integrated using a consistent framework based on Fashi’s typological hierarchy, archaeological measurements and visual references. The cumulative outcome was the reconstructed design of F1, which is summarised at the end of this section.

3.1. Design of Terrance

3.1.1. Layout and Function

To understand the design of the terrace, it was critical to clarify the function of the two protruding wings of its U-shaped layout. There was the possibility that these two wings faced either inwards towards or outwards from the walled core. On occasions when the wings faced outwards, they were called mamian (马面, literally horse’s face), as recorded in Fashi, serving both defensive and ceremonial functions—similar to a fortress bastion or the evolved que tower (阙, a freestanding, ceremonial gate tower), such as the Meridian Gate of the Forbidden City. Although there were existing qiaolou or gulou with mamian (Figure 8 and Figure 9) that displayed functions comparable to F1 as the main entrance of the prefectural yashu, the orientation differed, as these wings faced east. Archaeological research revealed that the cluster of either the prefectural yashu or the palace of the Great Xia regime was located to the east of F1 [3], suggesting that the two wings of F1 faced inwards towards the walled core. Openings on the east elevation linking the two guardrooms further confirmed this interpretation. It was therefore more likely that the two protruding wings of the terrace represented the remains of access ramps to the top of the terrace.

3.1.2. Height of Terrace

According to the remains on the site, large stone ashlars were used to build the foundation of the terrace, laid in a herder bond. The rammed earth at the upper part was walled with luyinqi (露龈砌, literally exposing gingiva bond, a stepped battering finish, bricks are laid in successive setbacks, creating a step-like profile). The thickness of each course including mortar was approximately 100 mm, and the batter angle was around 75 degrees. This corresponded to the regulation for city wall battering in Fashi: ‘Regulation of building city wall: increasing the thickness of the wall 20 chi at every increased height of 40 chi, and the thickness at the at decrease a half of the increased height. (筑城之制: 每高四十尺, 则厚加高二十尺。其上斜收, 减高之半。)’ [28]. For example, if the height of the wall was 40 chi, then the thickness of the wall at the foundation level was the 1.5 times the height, or 60 chi, and the thickness on the top was the thickness at the foundation level minus half of the height, which was 60 chi minus 20 chi, resulting in 40 chi. As the city wall battered on both sides, the setback was a quarter of the height. The arctangent of ¼ was 75.96 degrees, which was very close to the batter angle on the site. This demonstrated that the applied batter gradient of the terrace was 1:4. It also corresponded to the rough gradient of the rough finishing (粗垒, culei) of luyinqi, where each course was set back by 0.5 cun for every two-cun-thick brick course; however, the setback of each course on the site differed, as the bricks were not two cun thick.

As observed on the site, the brick finishing layer of the terrace comprised six layers of brick, with a total thickness of 36 cun. According to the regulation in Fashi, the finishing layer was specified to be five bricks thick if the building terrace was 20 chi to 30 chi in height, whereas it was required to be six bricks thick if the terrace was 40 chi tall or higher; however, no instruction was provided for cases where the terrace’s height was between 30 and 40 chi. Therefore, the height of the terrace was interpreted to be at least 30 chi [29]. We referred to a Southern Song monograph about fortresses, Shouchenglu (守城录, literally Records of Fortress Defence), ‘The city wall should not be too high, otherwise it is easy to be damaged by rain or water and collapse, and its construction is also labour consuming…It could be 3 or 3.5 zhang high. (城不必太高, 太高则积雨摧塌, 修筑费力……高可三丈, 或三丈五尺)’. As the remaining terrace on the site stood at 4.6 metres (approximately 14.8 chi) in height, the height of the terrace could either be 30 chi or 35 chi. For this study, 30 chi was adopted as the terrace height.

3.1.3. Interior Guardrooms

From the readings on the site, the distances from the centres of the easternmost and westernmost rows of postholes to the contour of the wall were approximately 75.5 cun and 75 cun; the distances for the secondary rows were 120.5 cun and 120 cun. Considering that the wall’s batter gradient was 1:4 and the column radii were 9 cun as stated before, the easternmost and westernmost rows of columns began to intersect with the brick finishing layer at a terrace height of 12 chi (3.72 m), and these columns pierced out from the terrace when the height reached 19.2 chi (5.952 m). The secondary rows intersected with the brick finishing layer when the height was 44.4 chi (13.764 m). As the columns in the terrace should be in the part of rammed earth instead of the brick finishing layer according to Fashi, the easternmost and westernmost rows of should not reach the top of the terrace, whereas the columns of the secondary rows did. It was inferred that there were two-storey structures inside the guardrooms and the easternmost and westernmost rows of the columns supported the floor of the upper storey (Figure 10). The interior wall surface creased to ensure a minimum wall thickness of six bricks.

3.1.4. Gateway

A dense distribution of postholes was discovered adjacent to the gateway at the site, with spacing at around every 1.5 metres. Considering such density of posthole distribution was not observed elsewhere at the site, we believe that the columns of these postholes not only supported the upper timber structures of the qiaolou but also related to the structure of the gateway. According to ancient paintings (Figure 11) and existing structures, the structures of gateways in the Song Dynasty were usually built in paichazhu (排叉柱, literally jamb column in row) timber frames with square columns and rarely with arch. Nevertheless, as there were no Song Dynasty remains that confirmed whether F1 employed either square-column paichazhu or arch-based construction, it was inferred that the structure of F1’s gateway was similar to the one of the South Qiaolou in Anhui, which was a cylindrical-column paichazhu (Figure 12).

Fashi stipulated that the columns of paichazhu were 2.4 zhang long, 1.4 chi wide and 0.9 chi thick, which corresponds to 7.44 metres long, 434 mm wide and 279 mm thick. Although cylindrical columns were believed to be adopted in F1, this standard length was adopted in this research. By adding the height of the foundation stone of the paichazhu frame, the height of the gate leaves would have exceeded 24 chi, or 7781 mm. The gateway remains on the site measured 7.17 metres, which was 23.13 chi, meaning that the width of the gate could not have exceed this measurement and the height of the gate leaves was limited to lower than this width of 23.13 chi, as in Fashi. As there was no conclusive evidence specifying the exact dimensions of the gate leaves, the width of each gate leaf was estimated to be 10.8 chi based on Fashi and existing historic structures [30], which is 3348 mm, and the height was estimated to be 25.1 chi, which is 7781 mm (Figure 13).

3.1.5. Access to Top of Terrace

As stated previously, the two protruding wings of the terrace were identified as the remains of a ramp providing access the top of the terrace. There were two types of access ramp recorded in Fashi—mandao (慢道, literally slow ramp) slopes and tadao (踏道, literally step ramp) steps. A mandao slope was paved with a serrated brick surface, whose gradient was 5:1, enabling horses and carriages to access the top of a terrace or city wall. The tadao steps had two types—brick-built and masonry-built. The gradient for a brick tadao was specified as 2.5:1, and that for a masonry tadao was 2:1.

The total longitudinal length of the terrace was 223 chi, and the two outer sides of the two openings towards the guardrooms were 93.5 chi as per the reading on the site. There was only 64.75 chi of length on one side of the accessing ramp. Even if an L-shaped turning was adopted, the length of the ramp would still be limited to 143.25 chi, counting the 78.5 chi on the transversal width. The height of the terrace was 30 chi, as analysed previously. If a mandao was adopted, its length would be 150 chi, which could not have been accommodated within the available space; if the 2.5:1 brick tadao was used, the width from the edge of the ramp to the southern end of the terrace top would only have been 24 chi, even when placing the start of the ramp at the edge of the guardrooms’ openings. This proportion was considered unreasonable, and the overall proportion of the 2:1 masonry tadao was believed to be relatively more coordinated. Therefore, the access ramp adopted in this research was defined as a 2:1 masonry tadao with a standard tread width of 8 cun and a riser width of 4 cun, as described in Fashi.

3.2. Design of Upper Timber Structure

3.2.1. Plan Layout

As it was a qiaolou, a timber structure was constructed on the top of F1’s terrace. The column grid layout of the upper structure corresponded with the terrace’s underlying grid. As previously inferred, the easternmost and westernmost rows of the terrace’s columns did not reach its top; therefore, the upper structure’s columns were supported by the inner four rows of the terrace’s columns, along with certain columns of the paichazhu frame. This indicated that the upper structure had seven longitudinal spans and three transversal spans, a scale which meets the hierarchy of F1 as a qiaolou (Figure 14). The detailed dimensions of the spans are presented in

Table 3. Dimensions of upper structure’s column grid.

Direction	Total Length		Span	Dimension of Span
	Ancient System (chi)	Metric System (m)		Ancient System (chi)	Metric System (m)
Longitudinal	127	39.37	Central	23	7.13
			Secondary	19.5	6.045
			Tertiary	19	5.89
			Quaternary (End)	13.5	4.185
Transversal	38	14.57	Central	19	5.89
			Peripheral	9.5	2.945

.

As the top of the terrace had almost not been preserved, little information could be obtained from the archaeological excavation. To infer the design of the upper structure, most of the evidence was drawn from Fashi, existing historic structures and visual materials, in addition to the archaeological findings. By referring to the upper timber structures of qiaolou or gate pavilions in the same era as F1, such as the east gate in Along the River During the Qingming Festival (Figure 10), Yanghe Pavilion (also transliterated as Yang-Ho Lou) in Hebei (Figure 15), etc., as well as existing studies [29,31], the upper structure was believed to be gable-and-hip roofed, situated over a pingzuo (平坐 or 平座, literally flat base) floor system on the top of the terrace.

3.2.2. Major Carpentry

As classified in Fashi, major carpentry (大木作, damuzuo) referred to the specifications related to the overall timber frame structure of the building, including beams, columns, framework, bracketing, eaves, rafters, etc. In contrast, minor carpentry (小木作, xiaomuzuo) concerned the non-load-bearing wood components, such as doors, windows, partitions, ceilings, coffers, wood balustrades, obstructing bars, niches, sutra cabinets, etc. According to the 10th century building manual Mujing (木经, literally Timberwork Manual), the structure of traditional Chinese architecture could be divided into three parts—upper (上份, shangfen), middle (中份, zhongfen) and lower units (下份, xiafen) [32]. The upper unit was the part above the beams, including the beams, purlins, rafters and roof framework, whereas the middle unit was the part above floor but under the beams, which mainly included the floor, columns and dougong (斗拱 or 斗栱) bracket system (Figure S1). As the timber structure of F1 was built on the terrace, the lower unit was the pingzuo system in this case.

The upper unit, the roof, was considered as the most distinctive feature in traditional Chinese architecture [25], representing the hierarchy of the building. The form and juzhe (举折, literally raise and depress, the curvature of roof slope) were the two most critical elements affecting the design of buildings’ roofs.

In terms of the form of the roof, the forms recorded in Yingzao Fazhi included si’e dian (四阿殿, literally four-slide hall, hip roof,), jiuji dian (九脊殿, literally nine-ridge hall, double-hipped roof), shaliangtou zao (厦两头造, literally design with penthouse at two ends, double-hipped roof), bu shaliangtou zao (不厦两头造, literally design without penthouse at two ends, overhanging gable roof), cuojian (撮尖, literally pinching into tip, tented roof), etc. Among these forms, si’e dian was used for diange with 5 to 11 longitudinal spans; jiuji dian was suitable for diange with 3 to 11 longitudinal spans; and shaliangtou zao was used for tingtang with 3 to 7 longitudinal spans and tingxie, whereas bu shaliangtou zao was designed for tingtang with 3 to 7 longitudinal spans, and cuojian was suitable for tingxie (

Table 4. Forms of traditional Chinese architecture roof and their suitable building types.

Form of Roof	Scenario of Application
Si’e dian	Diange with 5 to 11 longitudinal spans
Jiuji dian	Diange with 3 to 11 longitudinal spans
Shaliangtou zao	Tingtang with 3 to 7 longitudinal spans and tingxie
Bu shaliangtou zao	Tingtang with 3 to 7 longitudinal spans
Cuojian	Tingxie

).

As stated previously, F1 was defined as a tingtang, meaning that its roof would have adopted either a shaliangtou zao or bu shaliangtou zao form. Considering the fact that bu shaliangtou zao was usually used for lower-hierarchy buildings, shaliangtou zao was more suitable for F1 as the main entrance of a prefectural yashu. Moreover, the double-eaved roof design was restricted to use in imperial buildings, such as the main buildings of imperial palaces and temples, to demonstrate the power of the emperor [33]. A single-eaved roof was considered more likely to have been adopted, in line with F1’s prefectural hierarchy.

In terms of juzhe (举折, literally raising and bending), the definition of the roof’s curvature involved two steps—juwu (举屋, literally raising the roof) and zhewu (折屋, literally bending the roof) [32]. Fashi stipulated that the height of the roof to be raised was one third of the distance between the front and rear eaves’ purlins. The total transversal length (between the centres of the front and rear columns) of F1 was defined as 38 chi. As Tier 3 cai was used for F1, its total transversal length was 760 fen. According to the regulations in Fashi, the overhanging of eaves should be between 4 and 4.5 chi long. In this case, they were set at 4.2 chi, equalling 84 fen, and the distance between the front and rear eaves was 46.4 chi, or 928 fen. The height of juwu was 15.47 chi (4794.67 mm).

The zhewu was defined by the number of purlins according to the structural capacity. Fashi stipulated that the horizontal spacing of the transversal span should not exceed six chi, which was 120 fen, for Tier 3 cai. As there was a purlin at the ridge, the number of purlins would always have been an odd number. Typically, a Tier 3 cai building employed seven or nine purlins. For F1, if seven purlins were applied, there would be six transversal spans, each with a width of 156.67 fen, which did not meet the description in Fashi. If nine purlins were applied, the spacing between the purlins was 117.5 fen, which satisfied the requirement of remaining under 120 fen. As the height of juwu and the number of purlins were thus defined, the curvature of zhewu could be defined, and the parameters are presented in

Table 5. Parameters for F1 and corresponding specifications in Fashi.

	Specifications in Fashi	Parameters for F1
		In fen	In cun
Diameter of rafter	7 to 8 fen	8	4
Overhanging of eaves	4 to 4.5 chi	84	42
Feiyan (upturned eaves)	3/5 of eaves’ overhang	50.4	25.2
Diameter of column	36 fen	36	18
Height of eaves columns (peripheral row of columns)	7 to 10 times column diameter	336	168
Height of dougong	(1.4n − 1) cai − (n − 5) × a (n = number of puzuo (铺作), describing dougong size, equalling number of outwards huagong (华栱, also transliterated as hua-kung, transversal arms) and ang (昂, slanting member) plus three; a = constant value between two and five)	(1.4 × 7 − 1) × 15 − (7 − 5) × 2 = 128	64
Outwards extension of dougong	30 + 26 (m − 1) (m = number of outwards huagong)	30 + 26 × (4 − 1) = 108	54
Inwards extension of dougong	30 m’ (m’ = number of inwards huagong)	30 × 3 = 90	45

together with the specifications in Fashi (Figure 16).

According to these parameters, the total overhanging of the eaves (overhanging of eaves, feiyan (飞檐, literally flying eaves), and outwards extension of dougong) was 84 + 50.4 + 108 = 242.2 fen, which was 12.12 chi. This overhanging distance was larger than that from the centre of the easternmost and westernmost rows of columns to the contour of the terrace (12 and 12.05 chi). This met the functional requirement that the eaves should cover the terrace to prevent it from being flushed by rainwater (Figure 17) [9,29], thereby supporting the validity of the preceding inference.

In terms of the beams, there were two types described in Fashi—curved yueliang (月梁, literally crescent beam) and straight pingliang (平梁, literally flat beam). There was no specification regarding the circumstances under which either type should be used. By referring to comparable historic qiaolou buildings, the topmost beam was set as yueliang and the rest were designated as pingliang (Figure 18). The sizes of the beams are presented in

Table 6. Sizes of the beams of F1.

	Yueliang	Pingliang
	Topmost	Secondary Topmost	Rest
Width (fen)	42	42	45
Depth (fen)	28	28	30

.

In terms of the middle unit, the design of the columns could be inferred from the postholes found at the site. As the columns of the guardrooms’ structure and the paichazhu of the terrace were believed to correspond with the columns of the upper structure, the diameter of the upper columns was expected to be similar to or the same as that of the columns of the guardrooms and paichazhu, which was 18 cun. Though the height of the columns were not specified in Fashi, the ratio of diameter to height generally ranged from 1:7 to 1:10 according to known Song Dynasty buildings. The ratio was set as 1:8 for this study. Moreover, the shape of the columns was tapered at the upper end rather than being purely cylindrical, according to Fashi. The parameters of this shape were described in detail in Fashi, which this study followed.

There were two types of connection between the bottom of the column and the pingzuo system described in Fashi—chazhu zao (叉柱造, literally intersecting design) and chanzhu zao (缠柱造, literally entwining-column design). Chazhu zao created a cross-shaped lap joint between the columns of the two layers, whereas chanzhu zao involved placing the upper columns backwards on the beam framing the tops of the lower columns. This indicated that the upper and lower columns’ axes overlapped when using chazhu zao, and the axes parallelly separated with chanzhu zao. The plan of the upper structure was determined to be oblong based on the remains, whose ratio of longitudinal and transversal widths was approximately 3.3:1. If applying chanzhu zao, the width of each direction would shrink with the column diameter, making the plan even more elongated.

The design of a dougong was closely associated with the hierarchy of the building. Reviewing historic buildings from the 8th to 14th centuries (Tang to Yuan Dynasties), the greater number of puzuo or huagong, the higher the building was in the hierarchy. F1, as a landmark of the capital city of Chongqing Prefecture and the main entrance of the prefectural yashu, was believed to correspond to a similar tier as the east gate, a secondary city gate, of the empire’s capital city Kaifeng, which was realistically drawn in Along the River During the Qingming Festival (Figure 19). The gate’s dougong was depicted as a design with seven puzuo with double longitudinal gong (栱, also transliterated as kung, arms), double huagong and double ang on the outwards side. As the number of puzuo on the inwards side was stipulated to be one less than that on the outward side in Fashi, its inwards side design comprised six puzuo. Therefore, the same design of dougong was adopted for F1 (Figure 20), and the parameters are shown in

Table 7. Design parameters for F1’s dougong.

	Outwards	Inwards
Number of puzuo	7	6
Single or double longitudinal gong	Double	Double
Number of huagong	2	3
Number of ang	2	0

.

The dougong of a building could be classified into three types—zhutou puzuo (柱头铺作, dougong at the top of side columns), bujian puzuo (补间铺作, dougong in-between the columns) and zhuanjiao puzuo (转角铺作, dougong at the top of the corner columns). The distribution of dougong sets was required to be evenly spaced to ensure the harmony of façade design, as requested in Fashi, and the distance between dougong sets was not to exceed one chi, which was 20 fen, in F1’s case. Based on this requirement, three bujian puzuo sets were placed on the central span on the longitudinal elevation, two on the secondary and tertiary spans, and one on each of the quaternary (end) spans (Figure 21). For the transversal elevation, one set on the central span was enough to meet the requirements.

The lower unit of F1 included the terrace, which has been discussed previously, and the pingzuo system. The east gate in Along the River During the Qingming Festival and the Tang Dynasty frescos in the Mogao Caves (Figure 22) provided evidence for the existence of a pingzuo system between the upper timber structure and brick-earth terrace [10]. The dougong of a pingzuo system was described with one or two less puzuo according to Fashi, meaning that the number of puzuo for the dougong of F1’s pingzuo system should be five or six. As a pingzuo system with six puzuo could cover the top of the terrace, a feature commonly depicted in ancient paintings, but that with five puzuo could not, six puzuo were determined for the pingzuo system. The locations of dougong sets had the same footprint as the sets on the middle unit’s elevations.

3.2.3. Minor Carpentry System

Handrail Stairs. The handrail stairs in the minor carpentry system in Fashi were called huti (胡梯), with a gradient of approximately 45 degrees. There were two parts of F1 where huti were applied—the access towards the upper storey at the guardrooms inside the terrace and the entrance to the upper timber structure on both transversal elevations from the top of the terrace. Particularly, the access to the top of terrace could not utilise mandao slopes or tadao steps because of the limited spacing on the terrace’s top. Nevertheless, this ramp was possibly built from brick and masonry as remains of a stone-carved railing were found on the site.

Railings. Railings were named as goulan (勾阑) in Fashi, and various types of railing as well as their dimensions were recorded in detail. The stone railing discovered on the site indicated that a decorated railing, chongtai goulan (重台勾阑), was used for F1, but the exact location of this railing could not be confirmed. Considering the deadload of the masonry elements and the strength of the timber structure, this research argues that timber railings were applied to the part on and above the pingzuo system and stone railings were used for the rest of the building.

Doors and Windows. Lattice doors and windows were widely used in buildings from the 10th to 12th centuries, and are commonly found in the Song Dynasty architectural examples and paintings. This research adopted the square hollow pattern of lattice doors and windows and referred to the records of pozilingchuang (破子棂窗) window and lattice doors in Fashi.

Bargeboards. Bargeboards were important decorative elements on the roof of the si’e dian and jiuji dian in Song Dynasty architecture, especially xuanyu (悬鱼, literally hanging fish) and recao (惹草, literally attracting grass). The xuanyu could be either petal or cloud shaped, with a length of three to ten chi. In this research, the xuanyu was assumed to be cloud shaped, five chi long and three chi wide; the assumed recao referred to the drawing in Fashi, being 1.4 chi long and 2.7 chi wide.

3.2.4. Roof and Decorations

Tiles. There were two types of tiles for roofing used in ancient China—cylindrical tongwa (筒瓦, literally tube-shaped tile) tiles and plate banwa (板瓦, literally sheet tile) tiles. The cylindrical type was used only for higher-tiered buildings, while the plate type was solely used for lower-tiered ones. Specific requirements for tiles were described in Fashi: cylindrical tiles with diameter of 6.5 cun should be used for roofing according to F1’s hierarchy. However, a wadang (瓦当, head of cylindrical tile at the eaves) with a diameter of 165 mm was discovered at the site. This diameter was 5.3 cun according to the defined measurement system. As the diameter of the wadang should not be smaller than the cylindrical tile, the tiles used for F1 were considered to be one tier lower, with a diameter of five cun.

Roof Ridge. Roof ridges in Song Dynasty architecture were stacked with ridge tiles, instead of being bonded as in the 14th century or later. The height of the ridge was defined by the number of stacked layers, and the number of layers was designated according to the building’s hierarchy. According to the description in Fashi, the main ridge of F1 would have been 25 layers high (Figure 23), and its vertical ridge 23 layers high.

Chiwen. Chiwen (鸱吻, also known as shibi in Japan) are Chinese ornamental tiles set on both ends of the ridgepole that tops a shingled roof (Figure 23). The chiwen of F1 were stipulated in Fashi to be between five cun to 5.5 cun in height, and iron anti-bird spikes would not have been used.

Roof-figures and Decorations. There were various roof-figures and decorations recorded in Fashi, including shoutou (兽头, literally beast head), taoshou (套兽, lion head or dragon-head-shaped corner beam cap), kalaviṅka (嫔伽), dunshou (蹲兽, literally crouching beasts), huozhu (火珠, literally pearl with flame, decorative nail cap), etc., whose type, size and number were defined by the building’s hierarchy (Figure 24). Based on F1’s hierarchy, the following decorations were inferred to have been applied: a 3.5-cun-high shoutou, a taoshou with a diameter of eight cun, a 12-cun-high kalaviṅka, a set of four dunzhou with heights of eight cun and a six-cun-high huozhu.

The overall design of F1 is presented in Figure 25, which integrates the analytical results presented in

Table 8. Key major carpentry parameters of upper structure’s design, in metric system.

Longitudinal parameters	Number of spans	7
	Total length (mm)	39,470
	Width of central span (mm)	7170
	Width of secondary span (mm)	6030
	Width of tertiary span (mm)	5900
	Width of quaternary (end) span (mm)	4220
Transversal parameters	Number of spans	3
	Total length (mm)	14,580
Building module (cai)	Tier of cai	3
	Depth of standard-sized timber (cai, mm)	232.5
	Width of standard-sized timber (mm)	155
	Length of fen	15.5
Design of roof	Form	Single-eaved shaliangtou zao
	Number of purlins	9
Timber frame	Form	Tingtang
	Longitudinal beam framework	Eight-rafter span with continuous eaves supported by four columns
	Height of eave column (mm)	4464
	Diameter of column (mm)	558
Design of Dougong	Dougong at top of columns	Outwards: 7 puzuo, double longitudinal gong with 2 huagong and 2 ang Inwards: 6 puzuo, double longitudinal gong with 3 huagong
	Dougong of pingzuo floor system	6 puzuo, double longitudinal gong with 2 huagong and 2 ang

and illustrates the proposed restoration based on the modular dimensions and structural parameters derived from the archaeotectural analysis. The structure may be divided into two principal components: the lower brick-finished rammed earth terrace and the upper timber structure.

The terrace had a U-shaped plan, with a total longitudinal width of 69.1 metres and a transversal width of 24.4 metres. The thickness of its brick finish comprised six bricks laid in parallel, and the batter gradient ratio was 1:4. The terrace was 30 chi (approximately nine metres) high, and its top was connected to the upper timber structure with a pingzuo system using six puzuo dougong.

The upper structure had seven longitudinal spans and three transversal spans, with a total longitudinal width of 127 chi (39.37 metres) and a transversal width of 38 chi (14.57 metres). The column grid corresponded with the footprints of the postholes on the site. The column diameter was 18 cun, and its height was designed according to the diameter-to-height ratio of 1:8, making it 144 cun. The columns intersected with the pingzuo system with chazhu zao. The dougong design under the eaves was seven puzuo with double longitudinal gong, double huagong and double ang on the outwards side. The roof form was shaliangtou zao, with 25 layers of tile for its main ridge, decorated with chiwen at both ends. The eaves overhung by a depth of 12.12 chi (approximately 3.69 m), which was enough to cover the terrace. The decorative details included lattice doors and windows, xuanyu, recao and roof-figures such as shoutou, taoshou and kalaviṅka. The entire building conformed to the formal architectural standards of Southern Song official buildings.

4. Discussion

4.1. Architectural Typology and Functional Attribution

The classification of terraced building F1 as a tingtang aligned with both archaeological measurements and codified typologies defined in Fashi [27,28]. Although its spatial position and symbolic function as the main gate of the Chongqing prefectural yashu could suggest a diange typology, the modular standards employed, specifically the application of Tier 3 cai, more convincingly supported its classification as a tingtang. The column diameter of approximately 500 mm, inferred from posthole measurements, correlated with an 18 cun standard for Tier 3 cai, reinforcing this attribution.

This typological identification underscores the regional adaptation of architectural hierarchy in Southern Song frontier governance. While Fashi offered detailed prescriptions for building categories, the case of F1 demonstrates the flexibility with which these centralised standards were interpreted in response to local functional needs and material limitations. Such adaptation provides valuable evidence of decentralised architectural practices within a broadly standardised imperial system.

4.2. Correlation with Historical and Visual References

The reconstructed form of F1, including its U-shaped terrace and seven-by-three bay timber superstructure, demonstrates strong alignment with visual and material precedents from the Southern Song era. The layout and roof form (specifically the adoption of shaliangtou zao) correspond closely with representations in Along the River During the Qingming Festival and with surviving examples, including the South Qiaolou in Anhui and Yanghe Pavilion in Hebei. These comparisons affirm the validity of combining archaeological measurements with codified standards and historical imagery in archaeotectural reconstructions.

Moreover, the detailed dimensional modelling of roof curvature (juzhe), dougong configuration and column grid placement reflected a high degree of internal consistency with Fashi’s standards. The resulting reconstruction reinforced the utility of this hybrid methodology in cases where direct architectural evidence is fragmentary or absent.

4.3. Methodological Constraints and Interpretive Assumptions

A key challenge of this study lay in the absence of direct historical documentation regarding the original construction of F1. The building was constructed during a period of warfare and political instability during the Mongol conquest. Consequently, the reconstruction presented here was based on the archaeological findings and interpretive methods that integrate codified standards and visual–historical references. Despite the study’s reliance on measured data and textual verification, certain aspects of the reconstruction remained interpretive due to incomplete preservation. The placement of staircases and the identification of decorative components, such as chiwen, rely on analogy rather than direct evidence. These decisions were guided by consistency with standard practice as recorded in Fashi and verified through visual references, but they remain hypothetical within the limits of current archaeological documentation.

Beyond the absence of direct historical records, certain aspects of the building reconstruction were not addressed due to a lack of preserved physical or pigment evidence, such as interior decorations, material finishes and colour schemes. Although these features are integral to a comprehensive architectural understanding, they fell outside the scope of this paper’s architectural–structural framework, which prioritised structural form and spatial logic. The measurement system itself was statistically estimated and might reflect minor regional deviations. These limitations not only reflected the current state of preservation and available data but also highlighted important avenues for future research, including material analysis, residue testing and pigment recovery through chemical analysis or stratigraphic investigation. Furthermore, they suggest the potential for immersive digital reconstructions and comparative typological modelling to test spatial and ritual functions within similar Southern Song official buildings.

Additionally, regional construction practices, particularly in areas where few Song-period architectural examples had survived, might have introduced vernacular variations not fully captured in state construction manuals. While this study explicitly noted the interpretive nature of certain inferences, it also demonstrated how such reconstructions could be methodologically transparent and analytically rigorous.

4.4. Contribution to Archaeotecture and Broader Implications

This research made a significant contribution to archaeotectural scholarship by advancing a systematic and replicable framework for reconstructing historical architecture from partial evidence. By applying statistical analysis to estimate ancient measurement units and aligning physical data with historical design norms, the study enhanced methods for dimensionally accurate and typologically grounded reconstructions [7,18]. In contrast to prior studies that relied primarily on visual analogy or isolated typological classification, this study developed a quantitative reconstruction framework grounded in site-specific archaeological measurements and codified architectural standards. It thereby offers a replicable and methodologically transparent approach for the archaeotectural reconstruction of historical Chinese buildings, particularly in contexts lacking textual documentation. This synthesis not only enhanced academic rigour but also provided a model for interdisciplinary application across archaeological, architectural and digital heritage domains.

At the disciplinary level, the study advanced the understanding of how imperial construction standards were applied in regional contexts during the Southern Song Dynasty. It provided rare empirical insight into frontier administrative architecture, a topic underexplored in the existing literature, and positioned F1 as a case study for investigating the balance between ritual symbolism and pragmatic governance in architectural form. Beyond this case study, the integrated archaeotectural methodology demonstrated here could be applied to other archaeological sites in China where direct construction records are absent but fragmentary remains and codified architectural treatises exist. Moreover, the approach holds potential for cross-cultural adaptation in reconstructing historical architecture in other East Asian contexts where similar building systems guided traditional construction.

Finally, this work carries practical implications in the fields of digital heritage modelling and conservation planning. The transparent integration of archaeological and textual sources not only enhances the academic credibility of virtual reconstructions but also supports public interpretation, heritage tourism and educational applications aligned with contemporary cultural heritage management.

5. Conclusions

This study reconstructed the original design of the 13th century terraced building F1 at the Laogulou Yashu Archaeological Site through an archaeotectural approach that combined archaeological evidence with Song Dynasty construction manuals and historical visual references. The results produced a detailed model of a tingtang-type official qiaolou composed of a U-shaped rammed earth terrace and a seven-by-three-bay timber structure, conforming to Tier 3 cai modular standards and Song architectural typology.

The research offered three main contributions. First, it refined methodologies for reconstructing historical buildings by statistically estimating ancient measurement systems and applying them within a codified architectural framework. Second, it expanded knowledge of Southern Song official architecture, particularly in regional and frontier contexts where historical documentation is sparse. Third, it illustrated how centrally defined design standards were adapted locally in the material expression of governmental authority through architecture.

By bridging physical remains with codified design logic, the study strengthened both the scholarly rigour and interpretive clarity of architectural reconstructions. It underscored the potential of archaeotecture not only as a research method but also as a tool for site presentation and education. Future research could build upon this model through three-dimensional simulation, comparative typological studies across regional qiaolou and further analysis of construction logistics in ancient structures.