Tree-Ring Chronological Investigation on the Oak Poles of the Prehistoric Settlement of “Gran Carro” in Lake Bolsena, Central Italy: Landscape and Human Occupation

Abstract

Dendrochronological analysis was carried out at the archaeological settlement of Gran Carro, located in Lake Bolsena (Italy). According to the most recent archaeological evidence, the site dates back to the period spanning from the Middle Bronze Age (15th century BC) to the Early Iron Age (8th century BC). In the excavation of the archaeological area, wooden piles from deciduous oak species (Quercus section robur and Quercus section cerris) were found, species still common in the area. The analysed trees, aged 15–50 years, likely came from managed forests, though agamic regeneration is possible. Relative felling dates provide initial insights into the duration of the settlement phases, revealing modifications to the original structure over an interval year ranging from 9 to 23 years. Absolute dating using wiggle matching indicates that most of the analysed piles date between 934 and 810 BC, though calibration curve slope limits precision. Nonetheless, dendrochronological analysis suggests that the settlement associated with an individual dendrogroup can likely be placed more precisely within this time range from 907 to 885 BC. From a broader perspective, the excavated area so far indicates that the settlement can be dated with 95% probability to the period 1054–810 BC and with 68% probability to the period 1017–817 BC. The results represent a significant milestone and may offer valuable insights for future investigations and developments.

1. Introduction

Dendrochronology is currently recognised as the most accurate dating method in archaeology, allowing the dating of timber with (sub-)annual precision. Furthermore, it provides essential insights into wood provenance and the reconstruction of past landscapes [1]. In the study of prehistoric pile-dwelling settlements, dendrochronology is particularly suitable for interpreting the history of human occupation in the investigated area, timber supply and past landscape together with the evolution of wooden structures [2], especially when the groups of poles (cluster) of piles frequently lack evident spatial or chronological connection. From this point of view, dendroarchaeology is a multidisciplinary field that extends beyond absolute and relative dating, often integrating investigations in botany and forestry [3,4,5,6,7]. For prehistoric wetland settlements in the northern pre-Alpine lakes, dendrochronological research has been instrumental in documenting, with high chronological precision, the features and dynamics of lakeside settlement expansion phases [8]. Synchronisation of tree-ring sequences is also well known to facilitate the identification of repair and restoration phases in wooden structures [9,10] and in general also in pile-dwelling settlements.

The construction of prehistoric timber structures and pile dwellings primarily relied on locally sourced wood [11,12,13,14,15]. Even the simple identification of wood species contributes significantly to our understanding of the past landscape, allowing comparisons with current vegetation in the study area [16].

Tree-ring analysis, focusing on descriptive statistical parameters such as average annual ring width, can reveal the growth patterns of individual trees and provide information on the characteristics of the original forest stand. Tree-ring patterns often disclose cycles of forest exploitation (e.g., thinning and coppicing) and serve as a valuable tool for establishing the relative chronology of historical contexts. Synchronisation of ring sequences with established master chronologies remains the most effective approach for obtaining absolute dates for wood samples. The precision of this dating method depends on the tree species and factors related to woodcraft and post-depositional degradation [17]. The best approximation in wood dating is to find the felling date of the tree which has provided the analysed wood sample.

The highest level of accuracy is achieved when the felling date of the tree that sourced the sample can be determined. If bark or waney edge is preserved, the felling date can be identified with precision; otherwise, the determination of the actual felling time is less reliable and should be considered an estimate [9,17,18]. In many cases, archaeological wood remains are eroded at their outer margins, leading to the frequent loss of sapwood and bark. To address this challenge, efforts have been made to estimate the number of missing rings, particularly in species with easily recognisable sapwood, such as oak (Quercus spp.) [13,19]. In such instances, dendroarchaeologists typically determine a terminus ante quem non or terminus post quem, which approximates the earliest possible felling date [17,20,21].

When tree-ring series are too short for reliable dating and there are no absolute master chronologies valuable for the area under study, radiocarbon dating can be combined with dendrochronology, a methodology known as wiggle matching [9,20,22,23]. This technique mitigates the limitations of both methods, compensating for dendrochronology’s short sequences and lack of reference chronologies and radiocarbon dating’s high error margins and calibration curve irregularities. Wiggle matching thus reduces the uncertainty inherent in radiocarbon dating, especially for prehistoric periods, where the margin of error in radiocarbon alone can exceed a century [18,20,24].

Pile-dwelling settlements were typically built on lake shores, in marshy areas, or in depressions along valley floors and ancient lagoons. In Italy, pile dwellings are grouped into two main regions: the lakes of Northern Italy and the volcanic lakes of Central Italy, both of which have been extensively studied from the dendrochronological point of view [25,26].

In this work, we focused on waterlogged posts from the submerged settlement of “Gran Carro” in Lake Bolsena, Lazio region. It is considered the best-preserved protohistoric site in Central Italy because it is the only protohistoric site submerged since the Iron Age without subsequent reoccupation, a condition that has preserved its remains in an excellent state [27]. The site was identified as a Villanovian settlement, considered the earliest phase of the Etruscan civilisation [28,29]. Flourishing between the 9th and 8th centuries BC, the Villanovian culture emerged during the Early Iron Age in central Italy, primarily across modern-day Tuscany, Emilia-Romagna, and northern Lazio [30]. It is characterised by its distinctive funerary practices, settlement patterns, and material culture [29,31,32].

The “Gran Carro” settlement was discovered in 1959 by the mining engineer Alessandro Fioravanti and was excavated from the 1960s until the late 1980s in agreement with the Superintendency of Archaeology, Fine Arts and Landscape for the province of Viterbo and Southern Etruria (SABAP-VT-EM), also in collaboration with volunteer divers. Radiocarbon dating conducted in 1993 on ten wood samples from Gran Carro yielded calibrated dates ranging from the early 11th century to the mid-8th century BC [33].

In 2012, research at Gran Carro resumed with the adoption of new methodologies, including photogrammetry, enabling a 3D reconstruction of the excavated layers. These new excavations were integrated with topographical surveys to develop a complete archaeological GIS of the site. The results of these efforts facilitated a detailed reconstruction of the settlement’s occupation phases and a more refined analysis of the materials recovered [27]. Recent excavations under the Superintendence, have revealed that the site’s occupation period is much longer than previously thought [34,35,36], ranging from the Middle Bronze Age (15th century BC) to the Early Iron Age (8th century BC), with later phases of use extending to the 5th century BC in the Aiola, a stone structure that was only recently identified as a place of worship [34,35,36]. The primary objective of this research is to conduct a dendrochronological analysis of waterlogged wood samples from the Gran Carro settlement in Bolsena (VT, Italy). This analysis aims to enhance our understanding of the dynamics of pile usage within the “pile-dwelling” structures by grouping tree-ring series and offering insights into the land use and forest composition from which the analysed samples originated.

A total of 23 oak (Quercus spp.) piles were subjected to dendrochronological analysis to establish relative dating through tree-ring synchronisation and to achieve absolute dating using the wiggle-matching technique. This approach aims to narrow the absolute date range of the piles as precisely as possible, thereby providing archaeologists with valuable chronological information for future excavation campaigns and broader contextual studies.

2. Materials and Methods

2.1. Site Description

The wood analysed in this study was sampled from the underwater archaeological site of Gran Carro, located on the eastern flat shore of Lake Bolsena (42.591° N, 11.995° E) in the Lazio region of central Italy (Figure 1a). The settlement was initially established during the Middle Bronze Age (15th century BC), but the most substantial remains are attributed to the early Iron Age, between the 10th and 9th centuries BC, a period characteristic of the Villanovan culture in Central Italy [27].

In the immediate vicinity of the site, the lake shore is predominantly covered by oak-dominated woodlands, consisting of broadleaf forests and groves (Figure 1b), reflecting the natural vegetation surrounding the settlement area [37].

The settlement is remarkable for its exceptional state of preservation, with over 450 wooden piles still intact (Figure 1b), arranged in NE–SW-oriented parallel bands approximately three meters apart (Figure 2), comparable to the pile-dwelling settlements of northern Italy [38,39]. It was built on the shore of the lake, subsequently, the water level rose to cover the structures and eroded the piles at the same height at the water’s edge. The remains are currently located at a depth of 3.5 m [29]. Since the earliest excavations, two distinct shapes of pole tops have been documented—flat and pointed [38]. While the latter are attributable to the erosion caused by water, the flat ones show signs of cutting. Tools such as axes and saws were also recently found at the site (data still not published). Further analyses are awaited on the traces of use of the flat piles found at a certain depth under the seabed layers. It is noteworthy that the image in Figure 1b is quite similar to that shown by Bolliger, et al. [40].

2.2. Poles Sampling

Twenty-three wooden piles from the Gran Carro settlement were selected for this study. The upper portions of the poles were cleaned of sediment, and a cross-section approximately 5–10 mm thick was taken from each. The identification numbers (IDs) assigned to the samples correspond to those used by the underwater archaeologists: 002, 016, 036, 039, 050, 057, 125, 126, 133, 138, 144, 146, 152, 163, 170, 171, 173, 174, 177, 183, 189, 198, and 304. Their spatial distribution within the settlement is shown in Figure 2. The sampling area was selected by the SABAP-VT-EM in order to minimise disturbance to the archaeological site. In particular, the selection aimed to determine whether closely positioned poles belonged to the same construction phase and whether those farther from the identified group of poles (cluster) dated to different periods.

Microscopic examination conducted during a precedent study of the same research team [41] identified all samples as belonging to Quercus spp., primarily it seems section robur. However, some samples exhibited microscopic features more consistent with anatomical features of Quercus sect. cerris due to the thin cell wall and the specific distribution of vessels in latewood [41].

For each sample, the number of growth rings was measured along with the width of both sapwood and heartwood. The presence of bark or the waney edge was also recorded. Some poles are in a very good state of preservation. Wood degradation is quite variable with poles very well preserved [41] and other discs with the outer part quite damaged and collapsed [42].

2.3. Dendrochronological Analysis and Wiggle Matching

Ring-width measurement and dendrochronological synchronisation were performed using the TSAP-WIN™ software package (v. 4.89, Rinntech-Metriwerk GmbH & Co. KG^®, Heidelberg, Germany). Ring widths were measured along two radii for each disc with a precision of 1/100 mm. Descriptive statistics, such as the mean ring width and its standard deviation, were calculated. Each radial measurement was compared with its corresponding twin on the same disc and cross-checked with ring series from other samples. Both statistical and visual cross-dating were carried out following standard methodologies to ensure solid synchronisation.

Mean curves were constructed by identifying dendro-groups through visual and statistical cross-dating. The primary statistical parameters used for synchronisation were Gleichläufigkeit (GLK) [43], t-value Baillie–Pilcher (TVBP) [44], and t-value Hollstein (TVH) [45]. Additionally, the number of overlapping years (OVL) was considered to evaluate the length of the common interval between tree-ring series and interpret synchronisation results. The identification of dendro-groups allowed for the relative dating of samples, providing a means to cluster coeval wooden elements and distinguish different construction phases within the pile-dwelling settlement.

After forming groups of cross-synchronised tree-ring series, samples for wiggle matching were selected to accurately anchor the floating chronologies in time. Wiggle matching significantly reduces the relative error of radiocarbon dating by analysing samples taken at regular intervals along the tree-ring sequence (every 20–30 rings or at defined distances). By aligning sample positions with calibrated radiocarbon data, it is possible to precisely delimit the dating range and establish an absolute chronology. This absolute dating could provide a new reference chronology useful for future research and dating efforts.

For wiggle matching, six discs (036, 050, 126, 144, 189, and 304) were selected, with three to four specimens sampled from each for radiocarbon (¹⁴C) analysis [46].

The discs for wiggle matching were selected according to two main approaches. The first group includes samples from poles that are very close to each other and show good relative dating based on dendrochronological analysis (e.g., 126 and 144; 304 and 036). The second group comprises discs that are form poles not close to each other, but show good dendrocronological synchronisation (e.g., 189), as well as samples for which no reliable synchronisation—either statistical or graphical—could be established (e.g., 050).

The samples were analysed at the Centro di Datazione e Diagnostica (CEDAD) at the University of Salento, Italy. The radiocarbon results were calibrated to calendar years using OxCal software v. 3.10 (Oxford Radiocarbon Accelerator Unit-ORAU-Oxford, UK) [47,48], based on the INTCAL2020 calibration curve [22]. Wiggle-matching analysis was conducted following Bronk Ramsey, et al. [46].

3. Results and Discussion

3.1. Dendrochronological Analysis and Tree-Ring Pattern

Table 1. Xylematic parameters in the samples examined. ¹ SW: Sapwood; ² HW: Heartwood.

ID	Rings (yrs)	SW Rings 1	SW Rings (%)	SW Width (cm)	SW Width (%)	HW Rings 2	HW Rings (%)	HW Width (cm)	HW Width (%)	Mean Ring Width (1/100 mm)	Diameter (cm)
002	39	14	36	2.3	29.6	39	64	5.5	70.4	248.1 ± 109.1	19.35
016	29	7	24	3.1	25.6	22	76	9.0	74.5	401.2 ± 116.2	24.07
036	52	17	33	2.2	22	35	67	7.8	78	123.7 ± 36.9	12.37
039	45	20	44	2.7	37.8	25	56	4.5	62.2	161.6 ± 65.3	14.54
050	34	21	62	4.5	57.8	13	38	3.3	42.2	230.2 ± 73.2	15.65
057	16	10	62.5	3.7	54.4	6	37.5	3.1	45.6	389.3 ± 110.7	12.46
125	38	18	47	2.1	26.3	20	53	5.9	73.8	193.1 ± 76.8	15.06
126	50	17	34	1.6	21.3	33	66	5.9	78.7	160.6 ± 65.9	16.06
133	33	9	27	2	33.3	24	73	4	66.7	325.4 ± 154.0	21.48
138	17	7	41	2.7	39.7	10	59	4.1	60.3	398.9 ± 108.0	13.56
144	49	20	41	2.1	30	29	59	4.9	70	162.2 ± 66.6	15.90
146	15	8	53	0	0	7	47	7.3	100	429.1 ± 109.9	12.87
152	44	24	54.5	3.1	43.1	20	45.5	4.1	56.9	133.1 ± 50.5	11.45
163	15	-	-	2.5	48.4	15	100	2.7	51.6	344.0 ± 106.5	10.32
170	23	18	78	1.7	17.7	5	22	7.9	17.7	411.5 ± 92.5	18.93
171	21	9	43	1.9	22.9	12	57	6.4	77.1	357.8 ± 79.9	15.03
173	32	15	47	4.2	38.9	17	53	6.6	61.1	276.7 ± 116.1	17.71
174	23	6	26	3.9	37.5	17	74	6.5	62.5	514.7 ± 161.3	23.68
177	54	16	30	3.0	33.2	38	70	6.1	32.7	168.4 ± 75.4	18.18
183	21	9	43	2.5	27.2	12	57	6.7	72.8	472.2 ± 226.8	19.83
189	36	15	42	2.4	27.7	21	58	6.4	72.3	244.4 ± 101.8	17.59
198	16	5	31	2.7	32.5	11	69	5.6	67.5	453.1 ± 164.9	14.50
304	39	11	28	3.2	28.8	28	72	7.9	71.2	202.2 ± 67.0	14.15

presents the descriptive statistics of the analysed wood discs, including the diameter, total number of rings, sapwood (number of rings, radial percentage, and width in cm), heartwood (number of rings, radial percentage, and width in cm), and mean ring width. All the analysed discs belong to deciduous oak species. Most samples are attributed to the subgenus Quercus robur, although some exhibit anatomical features consistent with Quercus cerris [41].

The total number of rings per sample ranges from 15 to 54, with 19 samples having fewer than 40 rings. The number of sapwood rings varies between 7 and 24, while heartwood rings range from 5 to 35. The mean ring width spans from a minimum of 123.7 ± 36.9 (1/100 mm) to a maximum of 514.7 ± 161.3 (1/100 mm). The largest mean ring widths are observed in samples with fewer rings (e.g., samples 174, 183, and 198), while samples with more than 40 rings consistently exhibit smaller ring widths, generally below 2 mm. The diameter of the tree is from 10 up to about 25 cm. In nearly all samples, heartwood constitutes more than 50% of the total ring count, except for samples 050, 057, 146, 152, and 170. The variability in mean ring width may reflect differences in the growth conditions of the trees from which the discs were cut. Bark remnants are still visible in two samples, whereas the others have lost their bark, likely during the excavation process.

The dominance of oak in the poles of the settlement is unsurprising, as previous studies have shown that more than 90% of Bronze Age vertical piles were made from deciduous oak [49], owing to its favourable properties for construction. In the lakes of Northern Italy, the prevalence of oak in pile dwellings is attributed to the extensive deciduous oak forests in the surrounding hilly and lowland areas [25,26]. Similarly, archaeological evidence of oak in waterlogged remains has been documented in Central and Southern Italy, not only at Lake Bolsena but also at Lake Bracciano [50] and Lake Mezzano [49].

The analysis of growth patterns offers additional insights into potential land use practices and forest management strategies in the period and region from which the sampled trees originate. Samples with over 50 rings but relatively small diameters (e.g., samples 36, 126, and 177) exhibit growth patterns typical of seeded trees (Figure 3a). These patterns are characterised by slower and more regular growth, with occasional abrupt changes likely linked to the opening of gaps in the forest canopy at certain stages of the tree’s life. The young age of the poles, evidenced by the small number of rings (16–17) and the presence of wide rings, suggests that they may come from a coppice-managed forest [2,51]. The average radial growth rate and standard deviation in some samples are generally higher than those observed in high forest stands [52], this element needs also to be considered in order to make a hypothesis on coppice management (Figure 3b). Indeed, some observed qualitative wood anatomical characters, such as a lower vessel frequency, are consistent with the coppice management system according to the research of Girardclos, et al. [53] and Müllerová, et al. [54]. However, we cannot ascribe without any doubt all the samples to the coppiced oak trees because, in tree-ring patterns, a quite early decrease in ring width (samples 198, 057 and 38) was observed compared to a more prolonged high growth in coppice-managed trees [53] (Figure 3b). Coppice forestry has been a well-documented practice for centuries due to its ability to produce firewood and small-diameter timber within short rotation cycles [55]; however, the parameter tree age and the related diameter show an erratic distribution (Figure S1). This variability raises the question of whether the forest management was the result of deliberate cultivation or simply the incidental use of available timber.

Oak forests remain the most widespread vegetation in the area surrounding Lake Bolsena. However, forest management during the Bronze Age was likely diverse, involving both coppice and high forest systems [51,52]. This is consistent with the idea that humans exerted some degree of control over their environment starting from the Neolithic period. While the extent of woodland management at that time remains uncertain, it is believed that some form of structured intervention existed, albeit less deliberate and organised than modern forestry practices [51]. The fact that posts from archaeological settlements originate from trees of different ages and growth patterns, indicating heterogeneous and uneven-aged stands, has also been discussed in other studies [52,56].

Through dendrochronological cross-synchronisation, three primary dendro-groups have been identified (Figure 4 and Figure 5). Several tree-ring series exhibit strong synchronisation, confirmed by robust statistical results and visual alignment. Trees 174 and 198, however, show no synchronisation or affinity with the overall dataset, likely due to the brevity of their ring sequences. Figure 4 displays the bar diagram of the dendro-groups, highlighted in several shades of blue (M1 group), orange (M2 group) and green (M3 group). The color scheme presented in Figure 4 is consistently applied in the subsequent illustrations throughout the rest of the article. The groups are presented in chronological order, being M1 the earliest sequence. Some additional ring series, indicated in light-grey in Figure 4, exhibit less significant statistical correlations and visual similarity, suggesting potential extended groupings that may warrant further investigation. Synchronisation statistics for all mean chronologies are provided in

Table 2. Cross-dated statistical synchronisation within each dendro group M1 (highlighted in light-blue), M2 (highlighted in light-orange) and M3 (highlighted in light-green). Glk: Gleichläufigkeit value; GLS: Gleichläufigkeit level of significance (* p < 0.05, ** p < 0.01, *** p < 0.001); TV: t-value; TVBP: t-value Baillie–Pilcher; TVH: t-value Hollstein.

M1	057	304	M2	125	126	177	144	M3	173	189
002	Glk 93 GSL *** TV 2.7 TVBP 4.5 TVH 4.8	Glk 81 GSL *** TV 4.9 TVBP 7.3 TVH 6.0	039	Glk 75 GSL ** TV 4.1 TVBP 1.5 TVH 2.5	Glk 70 GSL ** TV 1.6 TVBP 3.5 TVH 3.0	Glk 72 GSL ** TV 5.1 TVBP 4.9 TVH 4.4	Glk 62 GSL TV 4.3 TVBP 2.5 TVH 2.1	036	Glk 68 GSL * TV 5.1 TVBP 3.9 TVH 3.7	Glk 54 GSL TV 4.2 TVBP 3.2 TVH 1.2
057		Glk 93 GSL *** TV 6.2 TVBP 3.4 TVH 10.5	125		Glk 68 GSL * TV 7.1 TVBP 2.6 TVH 2.7	Glk 74 GSL ** TV 2.2 TVBP 1.3 TVH 1.3	Glk 83 GSL *** TV 3.2 TVBP 4.1 TVH 4.2	173		Glk 68 GSL * TV 8.5 TVBP 2.7 TVH 2.6
			126			Glk 64 GSL * TV 4.3 TVBP 2.8 TVH 2.9	Glk 78 GSL ** TV 4 TVBP 4.7 TVH 3.8
			177				Glk 62 GSL TV 7.8 TVBP 2.3 TVH 2.1

.

When interpreting relative dating, it is crucial to consider the spatial proximity of the sampled posts. The excavation grid (Figure 2) covers an area with cells measuring 2 m × 2 m, and the maximum distance between investigated posts is about 8–10 m (SW–NE direction 173–304; NW–SE direction 144–171). The spatial arrangement suggests distinct patterns, with rows of posts running diagonally from post 304 to 138 and, on the opposite side, from post 177 to 173 along a SE–NW axis [27]. This arrangement is comparable to pile-dwellings in northern Italian lakes, where houses were constructed on frameworks of three rows of supporting piles, forming structures with dimensions of 3 m × 5 m or 4 m × 8 m [25] and it excavations of Neolithic pile dwellings across Europe—particularly in regions like the Alps, Italy, Switzerland, and Germany—have revealed recurring patterns in their layout and organisation [57]. However, currently, there is no definitive archaeological interpretation of the building phases at the Gran Carro settlement and it is not possible to establish at this stage a reliable comparison with other studies. By the archaeological research conducted between 2019 and 2024, it was evident that the residential area was built on dry land and that the structures rested directly on the ground [34]. This suggests that the site was a large lakeside settlement, but not elevated above the water; rather, it was founded on dry land and later submerged during the Iron Age due to a rise in lake levels [34]. The reasons for this rise remain unknown, leading the site’s discoverers in 1959 to mistakenly identify it as a “pile dwelling” [34].

The results of the dendrochronological analysis may provide crucial data for future archaeological investigations. Figure 2 reveals clusters of closely spaced posts. Some tree-ring series show excellent synchronisation, allowing for the construction of mean curves (e.g., M1 and M2). For instance, samples 002, 057, and 304 exhibit significant statistical synchronisation, with a GLK value exceeding 80% (Table 2). The bar graph indicates that posts 002 and 304 were felled in the same year, while post 057, which shows only 16 rings (six in sapwood), appears to be relatively dated 23 years earlier. However, we cannot exclude that pile 057 was felled in the same year as 002 and 304, as the outer sapwood rings could have been lost due to degradation.

A similar pattern emerges in dendro group M2, comprising samples 125, 126, and 144. These samples have approximately 50 rings each, yet the timeline of pole installation varies: tree 126 was felled 12 years after tree 144, while tree 125 was felled 21 years earlier. Based on ray measurements (Table 1), the diameters of these discs are estimated at 14–16 cm. Relative dating suggests that vertical posts were likely added in successive phases—it could be supposed in order to replace degraded posts or reinforce the original structure as the settlement expanded. Approximately 12 and 20 years after the initial construction, modifications to the settlement seem to have taken place, as inferred from the dendrochronological evidence. Notably, there was reinforcement of the original posts, with new roundwood material being added approximately 10 years after the initial construction.

Comparable findings were reported in a similar archaeological context. Billamboz [2] documented permanent occupation in pile dwellings for up to 60 years, with ongoing post maintenance and replacement, although the lifespan of individual constructions was typically short. On the southern shore of Lake Constance, the same author estimated continuous habitation of houses for around a decade [2].

Even short ring series, such as those from posts 050 and 128, exhibit good synchronisation, indicating they were likely cut at the same time. Synchronising short sequences remains a complex task and is often based on graphical comparisons supplemented by statistical analysis when possible [2].

3.2. Absolute Dating and Wiggle Matching

The absolute dating of selected posts using wiggle matching provides a partial but significant overview of the occupation period of the Gran Carro settlement. Four posts (189, 36, 144, and 50) exhibit terminal growth rings that fall within the period between 938 and 810 BC (Figure 6 and

Table 3. Selected rings for each individual sample and their corresponding calibrated radiocarbon dating.

Pole	Selected Rings	Calibrated Dating (2σ) (Year BC)
036	1–5	1106 1080 1055	(1.0%) (1.1%) (93.3%)	1096 1068 829
	16–20	981 939	(6.3%) (89.1%)	947 802
	31–3	1108 1086 1058 883	(2.1%) (2.6%) (81.8%) (8.9%)	1091 1064 889 834
	46–50	976 935	(3.7%) (91.7%)	951 800
050	1–5	1049	(95.4%)	832
	13–17	982 940	(6.8%) (88.6%)	946 803
	23–27	922	(95.4%)	800
126	1–3	1124	(95.4%)	897
	14–16	1044 1017	(1.5%) (93.9%)	1032 827
	27–30	1008	(95.4%)	823
189	1–3	993	(95.4%)	814
	12–14	1005	(95.4%)	820
	23–25	990	(95.4%)	811
304	1–5	1199 1131	(9.3%) (86.1%)	1141 926
	16–20	1211 960	(89.8%) (5.6%)	967 930
	31–35	1045 1019	(2.5%) (92.9%)	1029 830

) at a 95% confidence level. These results align with previous studies by Belluomini, et al. [33], which place some analysed posts between the 13th and 9th centuries BC.

The current wiggle-matching analysis refines this chronological framework, offering a more precise temporal definition despite the inherent challenges posed by the well-known Iron Age calibration plateau [56,58]. Specifically, posts 144 and 126, belonging to the same dendrochronological group, are likely dated between 907 and 885 BC (Figure 6 and Figure S2), representing the overlapping interval within the calibrated radiocarbon range. The results at the 68% probability level confirm this narrower time window and further strengthen the chronological assignment (Figure 6 and Figure S2, Table 3).

However, the absolute dating of the entire assemblage of posts discovered during the excavation requires additional corroboration through an expanded dataset and more solid graphical and statistical synchronisation. A more comprehensive sampling strategy would be essential to consolidate the current findings.

Wiggle-matching analysis provides a relatively precise dating range for the majority of the Gran Carro samples, placing them between 938 and 810 BC. By combining dendrochronological data, it is possible to refine the dating of dendro group M2 to the period between 885 and 907 BC. Indeed, radiocarbon (14C) analysis indicates that the settlement was likely inhabited for a longer period, extending further back in time. For instance, Pole 304, the furthest from the shore among the analysed samples, dates to between 1017 and 962 BC (at a 68% probability). Therefore, based on dendrochronological analysis and wiggle matching, the maximum possible time span for the settlement is between 1017 and 874 BC at 68% statistical probability, and between 1054 and 810 BC at 95% statistical probability. The radiocarbon calibration curve in that period is not very sloped; the few rings in the analysed samples and the number of samples analysed up to now do not allow us to refine the absolute dating of wood in the piles of the archaeological settlements.

4. Conclusions

The wood used in the posts of the Gran Carro structure belongs to deciduous oak species, which remain prevalent in the surrounding territory near Lake Bolsena. In the context of this study, oak is confirmed as the predominant species in archaeological settlements across Europe during the Bronze Age. In the case of Gran Carro, the structural feature consists of a pattern formed by posts arranged in rows at regular intervals. There are some corners that are marked by groups of poles positioned closely together, which may suggest a maintenance intervention due to wood degradation (although this hypothesis seems less reliable, given the very good state of preservation of the wood remnants) or an additional support structure designed to enlarge the original building. The maximum distance between the posts examined in the archaeological survey is 8 m.

Tree-ring patterns reveal distinct forest management practices, the most reliable is trees from seed regeneration but also agamic regeneration due for example to coppicing. The posts span a range of ages, from very young trees (15–16 years old) to trees approximately 50 years old. This variability raises the question of whether the forest management was the result of deliberate cultivation or simply the incidental use of available timber.

Dendrochronological dating identifies several dendro groups, suggesting that the structure may have been inhabited for more than 20 years. Notably, there was reinforcement of the original posts, with new roundwood material being added approximately 10 years after the initial construction. However, it cannot be excluded that smaller-scale interventions occurred over a shorter time frame, with the addition of smaller roundwood assortments. This hypothesis could be further assessed with a broader dendrochronological sampling and expanded wiggle-matching analysis together with further archaeological investigations.

Therefore, based on dendrochronological analysis and wiggle matching, the maximum possible time span for the settlement is between 1017 and 874 BC at 68% confidence level, and between 1054 and 810 BC at 95% confidence level. These results support the hypothesis that construction activity at Gran Carro occurred over an extended period, potentially lasting from 1054 to 810 BC. This means the wiggle-matching analysis ultimately places the Gran Carro settlement within the Late Bronze Age to the Early Iron Age, reinforcing its significance within the broader context of prehistoric settlement patterns in central Italy. However, the limited slope of the radiocarbon calibration curve during this period, the small number of growth rings in the analysed samples and the limited number of samples analysed examined thus far, hinder a more precise absolute dating of the wooden piles from the archaeological settlements. However, the results represent a significant milestone and may offer valuable insights for future investigations and developments.