Research on the Dynamic Defensive Efficiency of Traditional Military Settlements in the Ming Dynasty: A Case Study of Ningbo Coastal Defense, China

Abstract

Defensiveness is a pivotal characteristic of traditional military settlements in ancient China, influenced by various factors linked to settlement construction and the occurrence of battles. Previous studies have typically focused on specific periods or moments, overlooking the dynamic interrelationships that evolve over time. The study proposes the concept of ‘defensive efficiency’ as a specific indicator for measuring the level of military defense system construction. Meanwhile, the analytic hierarchy process (AHP) was introduced to decompose the complex defense efficiency indicators into a quantitative system consisting of four levels of evaluation factors, analyse and statistically analyse the individual evaluation factors, and finally integrate and visualise the comparison of the data over multiple periods of time with the help of a geographic information system (GIS). The results of the study show that the changes in defensive efficiency in the four periods reflected the four stages of coastal defense construction in Ningbo during the Ming Dynasty: the preliminary construction period, the full construction period after repeated Wokou infestations, the basic completion period, and the period when Wokou encroachments were reduced and the point of attack was relocated to the south. While the spatial distribution of battles drove the continuous construction and improvement of coastal defense settlements, the improvement of the coastal defense system had an obvious effect on resisting Wokou intrusion. The study enriches the understanding of the cultural significance of traditional Chinese military settlement systems, emphasises the importance of tailor-made strategies appropriate to different historical periods and regional contexts, and provides a basis for the sustainable conservation of extant remains.

1. Introduction

Defensiveness is one of the key characteristics of traditional military settlements in ancient China [1], ancient Rome [2], and many different civilizations [3,4]. During the long and turbulent dynastic changes in Chinese history, traditional settlements, in addition to their basic functions of production, living, religion, and economy, also developed the important characteristic of defensiveness [5]. This characteristic was not only reflected in actions such as building walls and setting up patrols but also in deeper issues of state institutions such as the military system. The defense of borders was of the utmost importance, which led to the formation of traditional military settlements in ancient China that were particularly defensive in nature.

Under the strict Du-Si-Wei-Suo military and political system of the Ming Dynasty, two lines of defense were formed: the military system of the Great Wall in the north and the military system of coastal defenses in the east—they were one of the most complex and complete systems of defense for military settlements in ancient China. These military settlements, spread along China’s coasts, were built to defend against invasions by sea pirates (Wokou) from eastern China. With a total length of over 3000 km from the Liaodong Peninsula in the north to Hainan Island in the south, they have left behind a diverse cultural heritage [6]. However, compared to the visible architectural representations of the Great Wall, which is a UNESCO World Heritage site, the Ming Dynasty coastal defense system has not attracted much attention due to the lack of a tangible material carrier [7]. Its strategic military value and cultural heritage have not yet attracted much attention, and the historical remains and conservation status are lagging behind.

Given the extensive coastline and complex terrain, military settlements needed to possess robust defensive capabilities. In the existing research on ancient Chinese traditional military settlements, there has been a substantial focus on the defensive construction of these settlements [8,9,10]. Qualitative studies have meticulously documented the construction history and spatial layout, discussing various defensive structures within the settlements, such as walls, fortresses, and watchtowers [11,12]. Throughout this process, the improvement of information collection methods such as GIS and GS has provided more possibilities for quantitative research [13,14,15,16]. Researchers have often explored the correlation between settlement locations and the natural environment, as well as the accessibility and defensive reach of these military settlements [17,18]. Then, an increasing number of quantitative research models have been applied, including the use of one or more methods such as AHP [19], CIRTIC [20], and PCA [21] for goal decomposition and the analysis of the internal influencing mechanisms of these settlements. The main reason for choosing AHP in this study is that, compared to objective assignment methods such as PCA, AHP allows for the adjustment of criterion weights through expert judgment, which is more in line with the decision-making logic of ancient military construction. However, most of these studies tend to concentrate on the spatial characteristics or construction features of military settlements at a specific point in time or within a particular region after they were established [22,23,24]. They often overlook the fact that, due to the ever-changing frontier conditions during the Ming Dynasty, the construction of military settlements was in a state of continuous evolution. The focal points of defense and the defensive structures themselves were constantly being adapted and modified. Thus, there remains a significant gap in the research concerning the dynamic changes in the defensive capabilities of military settlements over a given period.

In general, the level of goal achievement can be evaluated using the concept of “efficiency”. Efficiency refers to the ratio of the output of labour to the input of labour, or the amount of work completed per unit of time. “Defensive efficiency”, on the other hand, is a measure of the defensive capability of a military settlement system within a specific context [25]. For instance, constructing a highly defensible military settlement in an area with no conflict or building a weakly defensible settlement in a frequently contested stronghold are both examples of inefficiency. The defensive efficiency of a military settlement system is a complex composite index, including factors such as accessibility and the settlement’s construction quality, and is influenced by constraints like funding, resources, and policies. In response to previous research focusing on static situations in a certain time slice, this study further deepens the concept of defensive efficiency into dynamic defensive efficiency. Instead of moment-by-moment fluid dynamic monitoring, it emphasises adaptive adjustments and their efficacy transitions within the framework of a continuum of historical developmental stages.

The study attempts to quantify the dynamic changes in the defense construction of military settlements within a certain range by establishing the concept of ‘defensive efficiency’ and analysing the internal causes of these changes. This approach not only aids in a deeper understanding of the cultural significance of traditional Chinese military settlements and provides theoretical support for heritage protection and presentation but also offers insights into sustainable construction practices today.

2. Study Area

Because of its developed economy and abundant products, Ningbo became the primary target of Wokou’s covetous plundering, while its long coastline and complex and convenient water network made Ningbo a springboard for pirates to invade the mainland, leading to the unrest of the coastal people’s lives. As a countermeasure, the Ming government began to actively lay out the coastal defense line; coastal defense military settlement construction officially kicked off. The Ningbo area is one of the important main positions of the Ming Dynasty coastal defense system, and there are three reasons for choosing the Ningbo area as the research object:

(1)

Zhejiang defense area has always been the focus of the Ming government coastal defense construction, and Ningbo with the geographical characteristics of the Zhejiang coastal defense gateway (Figure 1) also naturally became the top priority of the Ming and Qing dynasty coastal defense deployment; the construction of coastal defense military colony has a high quantity and quality. Therefore, the coastal defense military colony system in Ningbo during the Ming Dynasty is very representative, and the quantitative analysis of the defensive efficiency of the Ningbo can reflect the construction law of the national coastal defense military colony system.

(2)

The comprehensive deployment and construction of coastal defense in Ningbo began during the Hongwu period of the Ming Dynasty. According to local historical records, the Ningbo area experienced 53 years of large-scale invasion during the Ming Dynasty. Therefore, the coastal defense of Ningbo has been in the process of dynamic improvement, with obvious dynamic and sustainable characteristics, which can reflect the ideas and strategies of resisting Wokou in different periods of the Ming Dynasty and can provide references for the study of other military settlements.

(3)

Due to Ningbo’s special position in China’s Ming Dynasty coastal defense system, a wealth of information has been left behind, laying the foundation for the defensive efficiency study.

2.1. Three Major Defense Areas of Ningbo Traditional Military Settlements

The Ningbo coastal defense system can be divided into three major areas according to the spatial relationship between the north, east, and south: First, the north is the Linguan defense area, which is dominated by Linshan Wei and Guanhai Wei. The second is the Dinghai defense area in the east, dominated by Dinghai Wei. The third is the Changguo defense area in the south, dominated by Changguo Wei [2]. The three major areas are delineated according to geographic units, and the layout of the military settlement system within each area also shows certain characteristics. As a relatively independent military region, the defense area has a complete combat system and can organise battles independently. At the same time, the defense areas are also closely linked and cooperate with each other to form a strict coastal defense line.

2.2. Ming Dynasty Ningbo Coastal Defense Battle Overview for Four Periods

During the Ming Dynasty, the intrusion of Wokou occurred almost constantly. In Ningbo, the main times of coastal defense are concentrated in the period from the Hongwu years to the Yongle years in the early Ming Dynasty, from the Zhengtong years to the Chenghua years and during the Jiajing years. The battles in different periods have different laws, and the defensive efficiency of military settlements also changed. Therefore, the division of the time periods is conducive to the comparison of defensive efficiency. The Ming Dynasty is divided into four periods of coastal defense with reference to the Mingdai Wokou Shilue. All the battles and their results recorded in the local records within the four periods were statistically and visually analysed and represented in the Ningbo coastal defense historical information map (Figure 2).

• The first period (1368–1521) is the period from Hongwu to Zhengde. As the Ming regime had not yet stabilised, Wokou invaded the southeast coast. Ming Taizu thus strengthened the maritime and land forces and established a solid coastal defense system. The coastal defense settlements—Weisuo forts in Ningbo—were established during this time. Marking the routes of the Wokou invasions, it can be seen that the two Wokou invasion raids in 1413 and 1439 had a large area of influence, even across war areas. It can be seen that the construction of the coastal defense system as a countermeasure must have a holistic mindset to achieve victory through the concerted defense between the war areas.
• The second period (1522–1557) is the middle and early period of Jiajing and the period of most concentrated Wokou aggression throughout the Ming dynasty. Compared with the early Ming period, the Jiajing period saw complex and significant changes in defense strategies. Therefore, the Jiajing Period is divided into two sections for comparative analysis. After the Hongwu Period, the peaceful marine environment led to a series of declining coastal defense constructions. In the early Jiajing Period, the coastal defense of Zhejiang and Fujian had been abandoned for a long time. The two coastal invasions in 1522 and 1523 forced the government to tighten the sea ban policy, but contrary to expectations, this triggered large-scale invasions in Wokou in the middle of the Jiajing period, characterised by a large number of times, long time, large scale, wide area, and repeated and winding routes. The defeat rate of the Lin Guan war area is significantly higher than the other two war areas; the scope of Wokou’s invasion even expanded into the interior, and the coastal defense system was significantly damaged. It can be seen that at this period, the expansion of Wokou’s power often made it impossible for a single coastal defensive Wei Suo fort to intercept and destroy them in time, and it was necessary for multiple coastal defense forts to work together.
• The third period (1558–1566) is the late Jiajing Period. In response to the Wokou Invasion, the Ming Dynasty began to take measures to strengthen the coastal defense forces. In particular, the defense systems of Zhejiang and Nanzhili were more complete. Both naval and land forces were stronger than before, and military settlements were repaired. Wokou’s power was also weakened. Coastal defense battles in Ningbo and the whole Zhejiang Province were significantly reduced.
• The fourth period (1567–1644) is the period from Longqing to Chongzhen. The force that remained in Wokou was no longer large, and the damage was relatively light. There were several attacks on the southern coast of Ningbo, which no longer poses a threat. By the end of the Ming Dynasty, Wokou was basically nonexistent near China’s coastal areas.

3. Methodology

The main methodology of this study is that after completing the establishment of the defensive efficiency evaluation system for the coastal defense of Ningbo in the Ming Dynasty, the defensive efficiency scores are compared with the historical facts, and in this way the evaluation system is verified to be reasonable and effective (Figure 3). Specific methodologies are described below.

3.1. Materials

The information on the Ming Dynasty coastal defense military settlements in the Ningbo region discussed in this article primarily comes from three sources. The first is the site information published online by the Ningbo Municipal Government based on China’s Third National Cultural Relics Census (available on the Ningbo and Zhejiang Cultural Heritage Protection website [26,27,28]) and related specialised publications. The second source is the comprehensive field surveys conducted by our research team over the past 15 years and the continually updated database on Ming Dynasty military settlements, including geographic and historical information. The dataset encompasses information on 12 large military settlements within four major defense zones in the Ningbo area, including 4 Wei forts (such as Linshan Wei Fort) and 8 Suo forts (such as Sanshan Suo Fort). The third category is related historical information. It is possible to collect not only settlement-related content but also information about the victories and defeats of battles. Relevant historical information includes local chronicles, coastal defense canonical books, general historical canonical books, coastal defense military books, atlases, and also coastal defense-related chapters extracted from the literature reflecting the life of the people in the Ming Dynasty. The specific bibliography can be found in the table in Appendix A.

3.2. GIS Analysis

In the 1980s, spatial analysis supported by GIS and computer technology began to be applied in archaeological research in western regions such as North America and Europe. Since the 1990s, it has been applied to the field of archaeology, including the traditional settlements research. This study mainly applies ArcGIS 10.8, using kernel density, cost distance, inverse distance weighted neighbourhood, viewshed analysis, etc., to obtain the contribution value of the defensive efficiency impact factors and to evaluate the scores.

3.3. Analytic Hierarchy Process (AHP)

Analytic hierarchy process (AHP) was first proposed by Professor T.L. Saaty of the University of Pittsburgh [29]. It is specifically designed to address decision-making problems involving multiple objectives, multiple criteria, and complex forms. AHP is a scientific research method for quantitatively determining the importance of each influencing factor. This method is widely used in planning and design, especially in situations requiring comprehensive evaluation to reach reasonable decisions [30,31]. The coastal defense military settlement system is a multi-variable system. Defensive efficiency, as a composite index reflecting both speed and capability, also requires separate analysis through layering and classification. AHP can effectively handle the multi-factor, multi-level problems in the quantitative analysis of defensive efficiency by scientifically calculating weight values [32]. Based on long-term research on the factors related to coastal defense military settlements, we attempted to comprehensively collect evaluation indicators that affect the defensive efficiency of military settlements. Using this method, an evaluation system was established based on AHP, with the defensive efficiency of the coastal defense military settlement system as the target layer (A) and the final score being determined by the intermediate layer (B) and the constraint layer (C) (Figure 3).

①

A_n: The overall objective of this study—the defensive efficiency of the coastal defense military settlements in Ningbo (A).

②

B_n: The overall objective is further divided into two intermediate indicators: the ability for mutual support among settlements (accessibility, B₁) and the military strength of each individual settlement (settlement forces, B₂).

③

C_n: This level further breaks down the intermediate indicators.

Accessibility (B₁) consists of three components: settlement accessibility (C₁), information accessibility (C₂), and postal delivery system accessibility (C₃), which examines the interconnectedness of the military settlement system, it can also be interpreted as the coverage of defense works and the speed of war response. As a systematic whole, the construction of coastal defense military settlements forms a networked layout, where the accessibility of each node in the network is key to the system’s rapid operation. The accessibility of core Wei-Suo forts (C₁) determines the ability of nearby Wei-Suo forts to provide support during warfare. Information accessibility (C₂), primarily through beacon towers, represents the early warning capability against pirate invasions. Additionally, the accessibility of the postal delivery system (C₃) reflects the efficiency of material transportation.

Settlement forces (B₂) examines the defensive constructions within the settlements themselves, divided into army power (C₄), which centres on the number of troops, and settlement construction (C₅), which focuses on the fortifications. Unlike the relatively static accessibility indicators, C4 has fluctuated significantly with changes in historical context and must be examined as a dynamic indicator according to historical timelines. This will be statistically analysed according to the four periods of Ningbo’s coastal defense previously mentioned.

④

D_n: At the C_n level, some factors can be directly quantified, while others need further breakdown. Information accessibility (C₂) includes the number of beacon towers (D₁) and the visual field of beacon towers (D₂). Settlement forces (C₅) include perimeter (D₃), wall thickness (D₄), wall height (D₅), land gates (D₆), water gates (D₇), watchtowers (D₈), Wopu (D₉, small huts built on top of the wall’s horse face for soldiers to shelter from the weather and store weapons), and moats (D₁₀).

3.3.1. Weight Calculate

Based on the established evaluation system, 20 experts in Ming Dynasty military settlements were invited to assess the importance of each layer’s evaluation criteria. Part of them are professors and associate professors who are deeply involved in the field and come from Chinese universities, totalling 10. Another part is the frontline staff of cultural relics protection departments in Ningbo and Zhejiang Province, totalling 10. During the preliminary fieldwork of this study, we contacted and cooperated with these frontline staff members, who were invited to fill out the AHP questionnaire. The evaluation scale is divided into five levels (

Table 1. Rating scale for the importance of evaluation factors in the judgment matrix [33].

Rating Scale	Importance
1	Of equal importance
2	Slightly more important
3	Significantly more important
4	Strongly more important
5	Extremely more important

). By comparing the importance of the evaluation criteria, a judgment matrix was constructed to derive the weight values.

Based on the expert scoring results, there are no significant weight differences among the elements in the A, B, and C levels. The changes in weights appear in the D₃–D₁₀ elements under C₅. For the time being, the other elements with no differences are equally weighted, and the weight judgment matrix for the D₃–D₁₀ evaluation indicators under C₅ is shown in

Table 2. D₃–D₁₀ layer judgment matrix.

	D3	D4	D5	D6	D7	D8	D9	D10	Wi
D3	1	2	2	3	2	5	4	3	0.249
D4	1/2	1	1/2	2	2	4	4	3	0.164
D5	1/2	2	1	2	2	4	4	3	0.194
D6	1/3	1/2	1/2	1	1/3	4	3	2	0.099
D7	1/2	1/2	1/2	3	1	4	3	2	0.136
D8	1/5	1/4	1/4	1/4	1/4	1	1/2	1/5	0.033
D9	1/4	1/4	1/4	1/3	1/3	2	1	1/2	0.046
D10	1/3	1/3	1/3	1/2	1/2	5	2	1	0.080

.

3.3.2. Consistency Test

The weight judgment matrix needs to undergo a consistency test. Let λmax be the largest eigenvalue of the judgment matrix, with its corresponding eigenvector being W_i.

$$\lambda max={\displaystyle \frac{\sum {\left(C_{5}W\right)}_i}{n{W}_i}}$$

(1)

Consistency Index: CI

$$CI={\displaystyle \frac{\lambda max-n}{n-1}}$$

(2)

Consistency Ratio: CR

$$CR={\displaystyle \frac{CI}{RI}}$$

(3)

Random Index: RI (

Table 3. Average random consistency indicator [33].

n	1	2	3	4	5	6	7	8	9
RI	0	0	0.58	0.90	1.12	1.24	1.32	1.41	1.45

). The evaluation method is as follows: if CR < 0.1, it indicates satisfactory consistency; otherwise, the judgment matrix values need to be adjusted to achieve consistency. According to the calculation, the maximum eigenvalue of the matrix is λmax = 8.43, and the consistency index CI = 0.062. Given n = 8, the table shows RI = 1.41. CR = 0.044 < 0.1 indicates that the results are consistent and the weight values are valid [34].

The weights of each layer are summarised and compiled to obtain

Table 4. Weights of defensive efficiency evaluation system.

A	B	WBi	C	WCi	D	WDi	Wi
A	B1	0.5	C1	0.33	-	-	0.167
			C2	0.33	D1	0.5	0.083
					D2	0.5	0.083
			C3	0.33	-	-	0.167
	B2	0.5	C4	0.50	-	-	0.250
			C5	0.50	D3	0.249	0.062
					D4	0.164	0.041
					D5	0.194	0.049
					D6	0.099	0.025
					D7	0.136	0.034
					D8	0.033	0.008
					D9	0.046	0.012
					D10	0.080	0.020

for the defensive efficiency of coastal military settlements.

3.3.3. Normalization

To standardise the scoring, we quantify the scores of each one into a percentage scale, 0 ≤ F ≤ 100. If the attribute is directly proportional to the score, the calculation is as follows:

$$\mathrm{F}={\displaystyle \frac{{\mathrm{C}}_{\mathrm{n}}\left(fi\right)}{{\mathrm{C}}_{\mathrm{n}}\left(fmax\right)}}\times 100$$

(4)

F is the quantified score after scoring; C_n(fi) or D_n(fi) is the attribute value of the settlement under the evaluation criterion; and C_n(fmax) or D_n(fmax) is the maximum value.

If the attribute value is inversely proportional to the score, the calculation is as follows:

$$\mathrm{F}={\displaystyle \frac{{\mathrm{C}}_{\mathrm{n}}\left(fmin\right)}{{\mathrm{C}}_{\mathrm{n}}\left(fi\right)}}\times 100$$

(5)

And C_n(fmin) or D_n(fmin) is the minimum value.

4. Results

4.1. Accessibility (B₁)

4.1.1. Settlement Accessibility (C₁)

The coastal defense fortifications were primarily established to protect against pirate invasions, with their locations strategically chosen to ensure interconnectedness, forming a robust defense system along the coast. Settlement Accessibility (C₁) measures the minimum distance between these settlements, which can be determined using the minimum cost distance analysis-based DEM in ArcGIS [35].

Table 5. Average minimum distance of Ningbo coastal defense settlements.

Defense Area	Military Settlement	Adjacent Settlement Cost Distance (km)	F1
Linguan	Linshan Wei	23.89	18
	Sanshan Suo	20.70	21
	Guanhai Wei	17.88	24
	Longshan Suo	19.12	23
Dinghai	Dinghai Wei	22.07	20
	Chuanshan Suo	16.84	26
	Guoju Suo	19.35	22
	Dasong Suo	25.46	17
Changguo	Qiancang Suo	17.09	25
	Juexi Suo	17.22	25
	Changguo Wei	13.17	33
	Shipu Suo	4.34	100

shows the cost distances between adjacent military settlements, from north (Linshan Wei) to south (Shipu Suo). Shorter distances result in higher contributions to defensive efficiency, thereby increasing the last score.

4.1.2. Information Accessibility (C₂)

As an important carrier of information, the layout of beacon towers is a key factor affecting the defensive efficiency, judged by the number of beacon towers (D₁) and the visibility (D₂).

For D₁, the beacon towers are marked and analysed by GIS density analysis to produce a kernel density map (Figure 4) to illustrate the spatial distribution pattern of the beacon towers. The beacon towers in the three main defense zones clearly form three clusters, with each cluster organised around its geographical centre as the core of its defense. The defensive layout of the beacon towers in the Linguan defense area is relatively compact along the coastline, while in the Dinghai and Changguo, the beacon towers are built along the mountains, tightly securing the coastline. The scores for D₁ are shown in

Table 6. Beacon towers of Ningbo coastal defense settlements (the information for the beacon towers are sourced from reference [36]).

Defense Area	Military Settlement	Beacon Towers	Number of Beacon Tower	F2-1
Linguan	Linshan Wei	Fang (jia)lu Beacon Tower, Daotang Beacon Tower, Zhoujialu Beacon Tower, Wupen Beacon Tower, Miaoshan Beacon Tower, Luojiashan Beacon Tower, Simen Beacon Tower, Zhaogang Beacon Tower, Xigaishan Beacon Tower, Hehuachi Beacon Tower	10	77
	Sanshan Suo	Xujialu Beacon Tower, Lishan Beacon Tower, Meishan Beacon Tower, Xushan Beacon Tower, Cuoyu Beacon Tower, Caishan Beacon Tower, Wujiashan Beacon Tower	7	54
	Guanhai Wei	Xiangtou Beacon Tower, Guashizhai Beacon Tower, Xilongshan Beacon Tower, Xinpu Beacon Tower, Guyao Beacon Tower, Xilongwei Beacon Tower	6	46
	Longshan Suo	Longshan Observatory, Shigongshan Beacon Tower, Longtou Beacon Tower, Longwei Beacon Tower, Shitangshan Beacon Tower, Qingxi Beacon Tower	6	46
Dinghai	Dinghai Wei	Gaoshan Beacon Tower, Zhushan Beacon Tower, Xiaoshan Beacon Tower, Luci Beacon Tower, Zhaobaoshan Beacon Tower, Dagushan Beacon Tower, Zhangshipu Beacon Tower, Dajiangang Beacon Tower, Dayuwan Beacon Tower, Changshanshan Beacon Tower, Zheng (gui) yu Beacon Tower, Lujuan Beacon Tower, Wangjialu Beacon Tower	13	100
	Chuanshan Suo	Qitou Beacon Tower, Suohou Beacon Tower, Baifeng Beacon Tower, Xishan Beacon Tower	4	31
	Guoju Suo	Santashan Observatory, Shengao Beacon Tower, Gaoshan Beacon Tower, Meishan Beacon Tower, Guanshan Beacon Tower, Xiakang Beacon Tower	6	46
	Dasong Suo	Daqian Beacon Tower, Kunting Beacon Tower, Hengshan Beacon Tower, Huangyan Beacon Tower, Citun Beacon Tower, Geao Beacon Tower, Jianqi Beacon Tower, Gangkou Beacon Tower	8	62
Changguo	Qiancang Suo	Qinglei Beacon Tower, Pumenling Beacon Tower, Dongmenling Beacon Tower, Zhongbao Beacon Tower, Qianshan Beacon Tower, Tuci Beacon Tower, Shanmu (yang) Beacon Tower	7	54
	Juexi Suo	Gongyu (Gongao) Beacon Tower, Banling Beacon Tower, Zhaoao Beacon Tower, Shatou (Shaling) Beacon Tower, Pingfeng Beacon Tower, Yuquan Beacon Tower, Wailing Beacon Tower	7	54
	Changguo Wei	Huangsha Beacon Tower, Songao Beacon Tower, Renyi Beacon Tower, Hejialan Beacon Tower, Houshan Beacon Tower, Qitou Beacon Tower, Wushi Beacon Tower, Qianshan Beacon Tower, Chikan Beacon Tower	9	69
	Shipu Suo	Houshan Beacon Tower, Qianshan Beacon Tower, Dajinshan Beacon Tower, Tuwan Beacon Tower, Songao Beacon Tower, Xiaao Beacon Tower, Fengjiashan Beacon Tower	7	54

.

For D₂, a larger viewshed of existing beacon towers indicates a stronger capacity for alerting against invasions. The placement of beacon towers must ensure a coherent flow of information within the effective range of visual or audible signals to effectively warn of enemy presence. D₂ serves as a visual evaluation index, representing the ability of beacon towers to communicate with each other and detect nearby enemies. By utilising the Viewshed tool in ArcGIS spatial analysis and loading the corresponding DEM elevation data [37], the viewshed range of the beacon towers can be determined (Figure 5).

In Figure 5, the green areas represent the visible range. The viewshed range of Linguan is the largest. Although the beacon towers defense layout in the Linguan region is farther from the coastline compared to other regions, the lower and relatively flat terrain of northern Ningbo still allows for full coverage of the coastline. In contrast, the Dinghai and Changguo regions are affected by mountainous terrain, requiring a higher density of beacon towers and optimised placement to meet visibility requirements. By calculating the visual field, the final D₂ scores are shown in

Table 7. Beacon tower visual index (D₂) of the coastal defense system.

Defense Area	Military Settlement	Visual Field (km2)	F2-2
Linguan	Linshan Wei	1070.33	22
	Sanshan Suo	2125.20	44
	Guanhai Wei	1661.19	34
	Longshan Suo	2932.95	61
Dinghai	Dinghai Wei	2446.91	51
	Chuanshan Suo	1730.92	36
	Guoju Suo	4838.76	100
	Dasong Suo	3764.12	78
Changguo	Qiancang Suo	748.32	15
	Juexi Suo	4137.89	85
	Changguo Wei	4000.91	83
	Shipu suo	371.80	8

.

4.1.3. Postal Delivery System Accessibility (C₃)

In the postal delivery system, the post road is the path of information flow, and the post station is the hub of the entire system. There are six post stations in Ningbo, namely Yaojiang Post Station, Chejiu Post Station, Siming Post Station, Lianshan Post Station, Baiqiao Post Station and Sangzhou Post Station. Since ancient postal route relics can no longer be traced, we first used the cost distance analysis to reconstruct the postal route network in Ningbo (Figure 6). Because material transport requires not only choosing relatively short routes but also avoiding difficult mountain paths and other challenging terrains, the cost distance calculation takes into account these terrain factors. This makes it more suitable for calculating the accessibility of the postal delivery system compared to straight-line distances.

The reconstructed postal routes avoid high elevations and generally run parallel to mountainous terrain. We select the cost distance from each military settlement to the nearest post station as the criterion for evaluating accessibility between each military settlement and its closest post station. Shorter distances indicate better accessibility and higher scores (

Table 8. Cost distance of postal delivery system.

Defense Area	Military Settlement	Cost Distance of Post Roads (km)	F3
Linguan	Linshan Wei	23.31	72
	Sanshan Suo	21.52	78
	Guanhai Wei	34.92	48
	Longshan Suo	21.86	76
Dinghai	Dinghai Wei	16.68	100
	Chuanshan Suo	44.11	38
	Guoju Suo	55.54	30
	Dasong Suo	36.41	46
Changguo	Qiancang Suo	78.31	21
	Juexi Suo	71.05	23
	Changguo Wei	65.33	26
	Shipu suo	71.89	23

). The results indicate that due to terrain influences, the military settlements in the northern Linguan sector are closer to the post stations, resulting in higher postal delivery system accessibility. In contrast, the Changguo sector shows a distinct disadvantage in postal delivery system accessibility.

4.2. Settlement Forces (B₂)

4.2.1. Army Power (C₄)

During the Ming Dynasty, the army power of coastal military settlements fluctuated over different periods. As shown in

Table 9. Number of troops in four periods.

Defense Area	Military Settlement	Army Power
		1st Period	F4-1	2nd Period	F4-2	3rd Period	F4-3	4th Period	F4-4
Linguan	Linshan Wei	5600	100	-	-	2445	30	1876	56
	Sanshan Suo	1120	20	535	16
	Guanhai Wei	5600	100	1283	39
	Longshan Suo	1120	20	531	16
Dinghai	Dinghai Wei	5600	100	3323	100	8040	100	3292	98
	Chuanshan Suo	1120	20	222	7
	Guoju Suo	1120	20	468	14
	Dasong Suo	1141	20	413	12
Changguo	Qiancang Suo	1120	20	925	28	2560	32	3344	100
	Juexi Suo	1120	20	1437	43
	Changguo Wei	4480	80	2808	85
	Shipu suo	2240	40	1445	43

, in the first period, during the initial construction of each military settlement, every settlement had a designated troop amount. The designated troop strength for a Wei fort was 5600 soldiers, typically overseeing five subordinate Suo forts. Some Wei forts, like Changguo Wei, only commanded four Suo forts; thus, their designated troop was lower than others. Generally, each Suo fort had a designated strength of 1120 soldiers. For example, Shipu Suo, which combined two Suo, had doubled the troops.

In the second period compared to the first, due to frequent conflicts, troop amounts in each military settlement were greatly reduced. By the second period, the troop strength at Lingshan Wei was no longer recorded, while Juexi Suo was the only one to see an increase in troop numbers.

In the third and fourth periods, there were changes in the Ming court’s military system. Troop numbers in each settlement were no longer fixed but fluctuated according to changes in military conflicts. Therefore, troop statistics were no longer recorded separately for each military settlement but aggregated by defense areas. This change in military structure somewhat improved operational efficiency and helped in containing invasions. However, Lingshan and Dinghai defense areas still suffered significant troop losses during conflicts. As conflicts moved southward, the naval construction in the Changguo defense area during the Wanli period led to a significant increase in troops.

4.2.2. Settlement Construction (C₅)

As the backbone of military defense, the various components of military settlements must coordinate closely to maximise their defensive capabilities. However, the construction of a fort was not accomplished in a single effort; it often required multiple phases of construction and partial repairs over several dynasties. This necessitates a phased analysis of C₅. Among the 12 Wei and Suo forts, the construction times, gate repair times, and wall repair times are all recorded in local chronicles. These repair records are concentrated in the first two periods of Ningbo’s coastal defense settlement construction, with minimal changes in the third and fourth periods. Yang provided a detailed overview of this in reference [25]. After multiple repairs, the construction status of these defensive settlements in the mid to late Ming period is shown in

Table 10. Impact factors of settlement construction (C₅).

	D3 (m)	D4 (m)	D5 (m)	D6	D7	D8	D9	D10 (m)
Dinghai Wei	4204.0	3.3	7.8	6	10	39	2185	3153.0
Chuanshan Suo	2421.9	3.3	6.9	4	12	12	1604	4357.4
Guoju Suo	1592.8	3.3	6.2	3	9	13	920	2859.3
Dasong Suo	2415.4	3.9	5.5	4	20	25	775	1083.6
Linshan Wei	2987.5	14.7	8.2	4	31	42	1142	2767.9
Sanshan Suo	1972	14.7	6.2	4	4	6	699	2154.2
Guanhai Wei	2399.8	9.8	7.8	4	28	36	1370	2983.3
Longshan Suo	1844.7	6.5	7.8	3	15	10	568	3368.4
Juexi Suo	1763.1	9.8	9.1	3	11	23	803	1044.5
Qiancang Suo	1763.1	4.2	8.5	4	12	20	1200	1958.4
Changguo Wei	4113.9	3.3	7.5	4	36	73	1914	705.0
Shipu Suo	1981.2	2.0	7.5	3	13	29	1906	359.0

. Based on the weights of D₃–D₁₀ obtained from expert ratings in Table 4, we calculate the scores of these influencing factors and the final scores of the C₅, as shown in

Table 11. The score of settlement construction (C₅).

	F5-3	F5-4	F5-5	F5-6	F5-7	F5-8	F5-9	F5-10	Final Score
Weight	0.062	0.041	0.049	0.025	0.034	0.008	0.012	0.02
Dinghai Wei	100	22	86	80	28	100	100	72	17.71
Chuanshan Suo	46	22	76	90	33	15	73	100	13.85
Guoju Suo	30	22	68	90	25	16	42	66	11.15
Dasong Suo	46	27	60	90	56	32	35	25	12.23
Linshan Wei	56	100	90	80	86	53	52	64	19.23
Sanshan Suo	37	100	68	90	11	8	32	49	13.78
Guanhai Wei	45	67	86	100	78	46	63	68	17.39
Longshan Suo	35	44	86	100	42	13	26	77	14.07
Juexi Suo	33	67	100	90	31	29	37	24	14.15
Qiancang Suo	33	29	93	70	33	25	55	45	12.42
Changguo Wei	78	22	82	80	100	92	88	16	17.27
Shipu Suo	37	14	82	80	36	37	87	8	11.61

.

To better illustrate the changes in the C₅’ scores of military settlements at each stage, we have plotted the variations in F5 based on the time points of each record (Figure 7). The results indicate that in the first stage, the basic construction of the forts in various Wei and Suo was generally completed during the Hongwu period. In the second stage, there was a concentrated repair effort during the Yongle period, resulting in a significant increase. A minor scale of repairs was conducted again in the mid-Jiajing period. Entering the third stage, F5 remained relatively stable by the end of the Jiajing period. We can also clearly observe that the defensive scores of Wei forts improved more significantly, particularly for Guanhai Wei and Linshan Wei. By the 44th year of Jiajing (1565), the defensive performance of the Wei forts had comprehensively surpassed that of the Suo forts.

4.3. Final Score

After obtaining the F for each impact factor, we calculate the scores by overlaying them with the weights and then compile the statistics according to the four periods of coastal defense in Ningbo. The results are shown in

Table 12. Final defensive efficiency score.

Defense Area	Military Settlement	1st Period	2nd Period	3rd Period	4th Period
Dinghai	Dinghai Wei	76.2	76.3	76.3	75.8
	Chuanshan Suo	43.4	42.4	45.9	52.4
	Guoju Suo	61.1	45.9	43.7	50.2
	Dasong Suo	44.5	43.5	47.0	53.5
Linhai	Linshan Wei	37.2	35.7	57.2	56.7
	Sanshan Suo	35.1	31.8	55.1	54.6
	Guanhai Wei	65.4	58.4	50.2	56.7
	Longshan Suo	39.4	37.4	59.4	58.9
Changguo	Juexi Suo	32.0	34.6	35.6	52.6
	Qiancang Suo	39.9	46.3	43.6	60.6
	Changguo Wei	60.4	61.6	48.4	65.4

. Then, we obtain the final defensive efficiency score for each military settlement in each period.

To more intuitively compare the differences in defensive efficiency of Ningbo’s coastal defenses across different regions and periods, we use the Inverse Distance Weighted (IDW) interpolation method in ArcGIS [38] to project the total defense scores of the coastal settlements in four periods onto a geographic coordinate system (Figure 8). The results indicate that Dinghai Wei in central Ningbo has consistently maintained the highest defense levels, while the defensive efficiency of other regions has shown significant variations over time.

By comparing Figure 9 with the historical map of Ningbo coastal defense battles (Figure 2), we can summarise the patterns and characteristics of the changes in the defensive efficiency of Ningbo’s coastal military settlements under different historical contexts.

In the first period, overall, the Dinghai defense area had the highest defensive efficiency, followed by the Linhai defense area and the Changguo defense area. Within the Dinghai defense area, Dinghai Wei had the highest score of 76.2 for defensive efficiency. Comparing the battle victories and defeats collated in Figure 2, Dinghai Wei has a higher probability of victory in this period. In addition, the imbalance within the Dinghai defense area is reflected in both the level of battle victories and defeats and the defensive efficiency. In this period, the defensive efficiency scores of Guanhai Wei, Dinghai Wei, and Changguo Wei were significantly higher than those of other regions; the defensive efficiency of Wei forts within each theatre was higher than that of Suo forts, and the difference in the scores was obvious, reflecting the idea of layered and obvious placement of military forces and accessibility under the hierarchical military defense system of Du-Si-Wei-Suo.

In the second period, the agglomeration within each defense area decreased, showing a more homogeneous development. This corresponds to a turbulent period when Wokou attacks and aggression were most concentrated, and the Chinese Ming government responded to this by beginning a comprehensive and intensive deployment of defenses, and the construction of more citadels began.

In the third phase, both the defensive focus and the centre of the battles were concentrated on Dinghai Wei. At this point, the differences in defensive efficiency scores within each defense area are shrinking, meaning that construction is almost complete.

Comparing the fourth period with the first three periods, it can be found that the defensive efficiency of Linhai defense area was gradually weakened while that of Changguo defense area was strengthened, indicating that the place where the battle took place moved from the north to the south, which is in line with the historical facts.

Through the comparison of the defensive efficiency scores of the four stages with the historical facts compiled in 2.2, it shows that the military settlement defensive efficiency scores can basically correspond to the historical facts, which verifies the validity of the method.

5. Conclusions

This study introduces the concept of “dynamic defensive efficiency”, establishes the evaluation system of China’s Ming Dynasty coastal defense military with AHP, takes Ningbo, China as the research object, and forms the dynamic research methodology of China’s Ming Dynasty coastal defense military settlement system, and obtains the following conclusions:

(1)

For AHP: Under the AHP system, the two factors, accessibility (B₁) and settlement force (B₂), are equally important in the defense efficiency according to the opinions of the interviewed experts. The more obvious difference in weight is the eight factors included in Settlement Construction (C₅), of which the highest weighted factors are Perimeter (D₃) and Wall Height (D₅), and the lowest weighted are Watchtower (D₈) and Wopu (D₉).

(2)

For the efficiency of China’s Ming Dynasty coastal defense: the changes in defensive efficiency in four periods reflect the four phases of the construction of China’s Ningbo coastal defense in the Ming Dynasty, the period of preliminary construction, the period of full-scale construction after repeated Wokou invasions, the period of basic completion, and the period in which Wokou invasions were reduced in large quantities and the point of attack was relocated to the south. Therefore, it can also be seen that, on the one hand, the construction of coastal defense in Ningbo, China during the Ming Dynasty was closely associated with Wokou invasions, and the spatial distribution of battles drove the continuous construction and improvement of coastal defense settlements, and that the Ming Dynasty was an important construction period for coastal defense in ancient China; on the other hand, the improvement of the coastal defense system had an obvious effect on the defense against Wokou invasions.

(3)

For the proposed methodology: the validity of the evaluation system is verified through the comparison between the AHP scoring results and the real battle victory and defeat situations in history, forming a reproducible set of quantitative methodology for the defensive efficiency of the Ming Dynasty coastal defense in China.

6. Discussion

The study focuses on the holistic and systematic characteristics of China’s Ming Dynasty coastal defenses and thus pays less attention to the specific roles of key defenses such as city walls, fortresses, and water systems. However, the various types of defense facilities of ancient Chinese coastal defense also have considerable traditional wisdom, which is worth expanding in detail and can be explored in depth as a future research direction.

At the level of heritage protection, the data collection and modelling in this study will be used to establish a more comprehensive heritage database, which will provide an important reference for subsequent heritage protection, restoration, display and sustainable development. At the same time, the parallel strategy of “digital twin + physical protection” is proposed to realise the visualisation of the defense scenarios through the construction of a digital twin system, which provides decision support for heritage protection and interpretation of heritage value. In terms of protection ideas, the systematic characteristics of the Ming Dynasty coastal defense suggest that in practice, it is necessary to break through the thinking of monolithic protection and instead establish an overall protection mechanism based on the cluster of settlements. Different specific protection strategies should be formed for different periods of Ming Dynasty coastal defense characteristics and military settlement remains. At the same time, it is suggested that the defensive efficiency should be incorporated into the value assessment system of military heritage, forming a dynamic protection path of “efficiency analysis—value determination—graded intervention”, and promoting the paradigm transformation of cultural relics protection standard from static value determination to dynamic efficiency assessment.