Letting the stones speak: An interdisciplinary survey of stone collection and construction at Liangzhu City, prehistoric Lower Yangtze River

Our interdisciplinary investigation of the stone collection and construction process of Liangzhu City walls offers important evidence to understand the engineering and organization behind the construction. We examined spatial distributions, physical and petrological characteristics of the stones discovered from our excavations of representative wall sections. These results were compared with similar aspects as well as sedimentation contexts and availability of the surveyed stones from the surrounding regions to identify the source areas for the stone collection. We developed criteria based on physical and petrological characteristics and spatial distribution of stones for the identification of construction units and estimated the volume of stones for each unit. We concluded that even though the overall scale of stonework construction was enormous, the actual tasks of stone collection and construction were likely completed by small individual working groups. Liangzhu workers preferred to collect directly available, hand‐portable stones from source areas. However, some areas with suitable stone sources were neglected by Liangzhu workers. The total workforce may have followed a central organization, and many groups likely worked simultaneously. Through the repeated efforts of numerous small working groups, Liangzhu society constructed a massive, multicomponent infrastructure. Our study holds implications for wider archaeological research of ancient stone architecture.

Natufian stone houses in the Levant (Boyd, 2006;Finlayson et al., 2011;Richter, 2017), the Neolithic Stonehenge in the UK , the classical-period palaces and monuments in Mediterranean (Broodbank, 2013), and more. Previously, predynastic China had been regarded as lacking stone architecture, but new discoveries of stone walls and buildings have radically changed these views. Among these discoveries in China, some of the most impressive examples include a Bronze Age fortified site of Sanzuodian in Northeast China (Shelach, Raphael, & Jaffe, 2011), the late Neolithic stone-walled site of Shimao in the Northern Loess Plateau (Guo & Sun, 2018;Jaang, Sun, Shao, & Li, 2018;Sun, 2016;Zhejiang Provincial Institute of Cultural Relics and Archaeology, 2005), and the earthen walls built atop stone bases at Liangzhu City of the Lower Yangtze River (Renfrew & Liu, 2018).
Research programs at ancient stonework sites have attempted to unpack their roles in the diverse trajectories of social complexity, addressing critical issues concerning how ancient people acquired and transported the stones, how they designed and constructed the monumental architecture, and how their complicated labor projects could have been organized (Boyd, 2006;Richter, 2017;Shelach et al., 2011). At the widely known site at Stonehenge, the research focus has shifted from the stone circle itself, instead now considering the larger surrounding landscape for a holistic understanding of the construction process . With this conceptual expansion, the individual stone components of Stonehenge have been situated in their original provenances and reinterpreted as instruments in "feeding" the monument (Craig et al., 2015;Darvill, Marshall, Parker Pearson, & Wainwright, 2012). The bluestones and sarsen stones have been analysed in terms of their petrological properties, measurements of the stone tonnage, and other variables that in concert have depicted the ancient transportation routes and techniques of bringing these components to the site (Harris, 2017;Parker Pearson et al., 2015).
While it may never be known about the exact actions during ancient times, the studies at Stonehenge and elsewhere have been instructive for establishing new research programs about ancient stonework sites such as in our current example at Liangzhu (5300-4300 B.P.).
To understand these similar issues, our interdisciplinary study examined the geophysical compositions and engineering design of ancient stone wall bases and other features of Liangzhu City, regarded as one of China's most spectacular ancient cities.
Liangzhu culture is characterized by its advanced jade industry, and its highly stratified society demonstrated by the rich jade-bearing elite tombs and a developed regional network on the distribution of elaborate jade items (Qin, 2013;Renfrew & Liu, 2018). While the control of jade resources and jade production at Liangzhu City is widely considered a unique trajectory to social stratification at Liangzhu and thus has received intensive scholarly attention, the acquisition patterns of stones and other construction and economic resources at the city are much less well understood. The labor organization and its implications to social complexity in Liangzhu society remain unclear.
Our research, conducted by field archaeologists, geologists, and petrologists, combined three lines of evidence to reconstruct the raw materials acquisition and mobilization into extensive stone wall bases at Liangzhu City. We obtained evidence of spatial distributions, physical characteristics, and petrological properties of construction stones through our excavation of selective stone wall sections and on-site observation. These multiple lines of information helped us identify construction units. We then surveyed possible source areas where the construction stones might have come from, focused on the physical and petrological characteristics as well as sedimentation contexts and availability of stones in these areas. Comparing this information with the examination of construction stones enabled us to determine stone collection procedure and provenance the construction stones. Here we present detailed information regarding how this study was conducted. We then discuss how the results helped us to comprehend the labor organization and construction process underpinning the construction of the enormous earthen and stone works at Liangzhu City.

| Building Liangzhu City and its walls
Liangzhu City is situated in the so-called C-shaped basin to the south of the Taihu Lake region of the Lower Yangtze River (Figure 1a). It is surrounded by the Tianmu Mountain ranges to its north, west and south. The modern East Tiao River runs across the northwest and north corners of Liangzhu City (Figure 1b). Liangzhu society predominantly relied on rice agriculture, as attested by the discovery of thick carbonized rice deposits of several dozen 1,000 m 2 inside the city and a well-preserved paddy field (c. 80 hectares) at Maoshan (Zhuang, Ding, & French, 2014). The surviving architectural components at Liangzhu City include a palace compound built on a large artificial platform, several elite cemeteries on artificial platforms or altars, enormous storage facilities filled with abundant carbonized rice remains, piers, and numerous other features. The ancient piers were connected to an extensive water management system inside and surrounding the city, including at least 51 artificial and natural canals and ditches (Liu et al., 2017;Liu, Qin, & Zhuang, 2020;Figure 1b). Additionally, an enormous hydraulic enterprise was constructed just outside the city, where high and low dams formed large-sized reservoirs, along with extensive levees (Liu et al., 2017).
The massive constructions at Liangzhu City have prompted questions about the extent and organization of their underlying labor and resources (Liu et al., 2017). The entire enclosed area of the city measured around 290 ha. The central Mojiaoshan palatial compound occupied 30 ha and required about 2.28 million m 3 of moved earth. On an even larger scale, around 2.88 million m 3 of earth would have been dug and transported to build the Tangshan levees, low dams and high dams of the hydraulic enterprise (Liu et al., 2017).
These impressive constructions of Liangzhu City reflect two architectural technologies. First, people dug clay from swampy lands, and they wrapped the clay into bundles with grasses (Chen, 2019). These "sandbags" were stacked to raise the ground and to fill the cores of walls and mounds ( Figure S1) which were then dressed or stacked by multiple layers of yellow silty clay. Second, people built stone bases as the supporting foundations for the stacked earthen layers. This technology can be seen in the construction of the city walls and the Tangshan levees ( Figure S2).
The positions and layouts of Liangzhu's city walls have been confirmed as two "circles" of inner and outer portions, as seen through aerial imagery and ground-truthing surveys (Figures 1b and 2e).
The contiguous inner-circle walls formed an overall rounded-cornered square in plan-view, measuring around 1.8-1.9 km south-north by 1.5-1.7 km east-west. Extending outward to the east and south, the outer-circle walls formed an irregular shape in plan-view, with maximum dimensions of 3 km × 1.7 km.
Excavation trenches have exposed the construction techniques of the city walls. Stone bases were observed in all cases, and those base constructions can be extrapolated as a total 29 ha of stonework for making the city walls. The single-layered stone bases, 40-60 m in width, were emplaced in a grayish clay (c.20 cm in thickness) that formed a mucky ground, at least during wet seasons, and therefore, a stone base solved the immediate concerns for creating usable foundations. Furthermore, stone material allowed water to drain downward through the stonework interstices and into the natural water table, whereas simple mounded earth would have slumped and subsided in this environment.

| METHODS AND MATERIALS
We considered spatial distributions, physical and petrological characteristics of the construction stones during our excavation and onsite observation. Similar features as well as sedimentation contexts and availability of stones were observed during the field geological survey. These different research activities were designed and conducted together by all the project members. Different lines of evidence were collected, shared, and discussed between different specialists, leading to our successful identification of construction units and stone provenance. The roles of project members are illustrated in the flowchart ( Figure 2) and explained in detail below.
We excavated a total of more than 700 m 2 in representative portions of the eastern, western (two excavation trenches in the western wall), northern and southern walls of the inner circle ( Figure 3 and Table 1). Excavation at the western wall was particularly informative, revealing about 500 m 2 of the stone bases. The excavation revealed how the stone bases were paved, whether the stones faced the same or different directions, and whether they can be divided into different piles or units. This information, combined with the measurement of the stone physical and petrological characteristics, provided key evidence for the identification of construction units. The measurement of physical and petrological characteristics of the construction stones was based on our extensive on-site examination of almost all of the 10,526 pieces of stones. The physical characteristics include size, shape, and roundness. Regarding the size, as we were not able to move or turn over the stones, we only measured the long and short axes and calculated the ratio of the long and short axes of the exposed surface of the stones. Square, elongated, or other shapes of the stones were documented. Stone roundedness was recorded in categories of subangular, subrounded, and rounded shapes that could be coordinated with the original depositional processes of the stones before they were collected. Stones of rounded shape are transported for a long distance, while angular shapes suggest stones are either broken in situ due to natural weathering and/or mined directly from bedrock. Stones of subangular or subrounded shapes indicate that they experienced a moderate degree of abrasion from short-distance transportation. In addition, for very few stones that showed damaged edges, we applied the technique of continuous shooting of highmagnification photographs to closely examine these sharp edges.
The petrological characteristics of the construction stones were recorded in situ during excavations, including color, texture, weathering, mineral assemblage, and structure. These attributes allowed the stones to be assigned in several objective groups. Those groups feedback to the information obtained regarding the spatial distribution and physical characteristics of the stones, corresponding with spatially distinctive patterns of construction units that were completed by different work groups during different events or tasks.
Our geological survey expanded on an initial analysis of geological maps and satellite images and results of previous field observations. Geologically, the Tianmu Mountain ranges are dominated by Cretaceous granites, intrusive rocks, volcanic rocks, middle Jurassic terrestrial sedimentary rocks, and early Paleozoic marine sedimentary rocks (Table S1).
The field-walking routes prioritized locations with bedrock outcrops or other stone source exposures ( Figure S3). We focused on three im- and roundness) as well as assemblage (whether stones in each landform unit tend to belong to limited or highly mixed rock types) of stones in the surveyed areas. We then identified and recorded characteristics of texture, structure, weathering, and other objective attributes of stone samples we found on the surface or embedded in the sediments in these areas. The physical and petrological characteristics of surveyed stones were then compared with those of construction stones. The comparison provided key evidence for stone provenance. Furthermore, the assessment of the stone availability helped us to determine stone collection preference and procedure. To further corroborate evidence on stone raw material provenances, we selected ten stone samples from both the construction areas and surveyed regions for detailed geochemical analysis. For more detailed definition of stone geochemistry, ten representative pieces were selected from the excavation and field survey, and the analysis produced corroborating evidence for stone pro- 3 | RESULTS

| Characterizing the construction stones
Our on-site observation shows that individual stone pieces were predominantly square or nearly square, while elongated pieces were selected only rarely. The ratios between the length (long axis) and width (short axis) mostly were between 1 and 1.8, but a few outliers reached values of 2 or more ( Figure 5b). The ratio of the length (long axis) and width (short axis) indicates whether the stone is of square or spheroid shape (when the ratio is close to 1) or elongate shape (when the ratio is larger than 1). As shown in Table 2, the majority of stones measured between 10 and 35 cm in length and weighed around 5 kg, while only small percentages were either larger than 40 cm or smaller than 10 cm ( Figure 5a). Differential groupings of stone dimensions can be discerned for the separate walls and construction segments. The sizes of the stones generally were smaller (10-15 cm) in the east wall, while they were longer (mostly 15-20 cm but occasionally 50+ cm) in the south, north and west walls ( Figure S4).
According to our recording of their roundedness ( identified, and they could be described as rounded pebbles ( Figure 6).
Our observations furthermore revealed that the majority of the stones were not altered by mining tools that otherwise would have created angular edges. Except for a few rare larger chunks of stones that were broken into smaller suitable pieces, nearly all of the construction stones had been used in their raw forms from surface collection. The very few broken pieces showed signs of damaged edges, possibly attributable to breakage during collection or transport. Of 20 samples that appeared to have been edge-damaged, detailed examination with the technique of continuous shooting of high-magnification photographs under microscope confirmed that 16 of those 20 pieces indeed were chipped and smashed. It also should be noted that some stones experienced severe postconstruction weathering, which caused sharply broken edges. Such edges, however, can be easily differentiated from the edges created by chipping or smashing during stone collection just described.
In our petrological examination, the construction stones belonged to a diversity of sedimentary, metamorphic, and igneous rock types in 11 distinctive categories (Table S2)

| Identification of construction units
In most of the excavated trenches, the stones were more or less evenly and horizontally aligned (Figure 3c These areas were separated by clear boundaries according to their different rock types and stone alignments. In the southern-wall excavation trench, the exposed stone bases were identified as belonging to 10 construction units (Figure 8). Most of the identifiable construction units were 1.5-3 m in width. Only two of the construction units were significantly larger than the others, measuring 5 m (unit 9) and 9 m (unit 10) in width, respectively. Each unit tended to use a limited range of stone raw materials, but there were exceptions. Stones in unit 2 (1.5 m in width) were divided into two piles. While most stones belonged to rhyolitic vitric tuff (blue colors in Figure 8), there were a few rounded-shaped quartz-sandstones, trachyandisitic crystal ignimbrite, and silicified rock scattered in the small pile in the west. More than 50% of the stones in unit 6 (2 m in width) were quartz-sandstones, with many rhyolitic vitric tuff and silicified stones mixed in them. Unit 9 is 5 m wide, but only covered by some silicified stones.
Another kind of distinctive construction event was exposed in

| Sourcing the stones
The geological field surveys of Areas A, B, and C contain wide-range geomorphologic units (Table 4)  In these three areas, 22 lithological groups were identified (Table S1), deposited in different landforms and diverse sedimentation contexts (Table 4) (Table 4).
The information of sedimentation, distribution, physical features, and assemblage documented during our survey provides key evidence to compare with the same variables of the construction stones.
As introduced in Section 3.1, most construction stones are square or nearly square, subangular or subrounded, and c.10-35 cm in length.
Based on this information and the fact that stones of the same petrological features tend to appear in the same construction units (Section 3.2), mountainous valleys and low mountains in the surveyed areas A and B must have been the most likely source areas supplying stones to the five excavated construction sites. The characteristics of stones from these two landform units (Table 4) are similar to those of most construction stones revealed in our excavation. In terms of lithological origins, these stones belong to eight of the 22 lithological groups (Table 5).
T A B L E 4 Distributions, and depositional characteristics and preservation of different types of rocks in the surveyed geological areas Further details were ascertained through thin-section and geochemical compositional analyses. Thin-section analysis showed nearly identical microscopic petrological properties between the construction stones and some of the surveyed stones (Figures 11, S7, and S8).  (Table S1).
The neglect of certain stone sources may have been due to cultural considerations, choices that we cannot identify based purely on our geoscience approach. For instance, stones from the Qianligang group (QLG) were excluded from usage in the walls, yet they provided the raw material for the stone tool production at Liangzhu sites. Admittedly

| Labor organization of stone collection and construction
The Liangzhu workers were armed with few tools but most importantly with an awareness of what kinds of stones they needed and where to collect them. With this knowledge, a small team did not need to devote much time to collect the stones. We conducted a preliminary assessment of possible transportation routes and transportation tools (e.g., bamboo rafts that have been found at Liangzhu sites, Figure S6) for the Liangzhu workers to transport the collected stones to the construction sites. However, as these results are preliminary and need to be supplemented by more evidence, we will report them separately.
After a unit of stones arrived at the designated construction area, we suggest that the collected stones were unloaded directly to build the stone bases. Each construction unit of stones would be enough to build around 4-5.2 m 2 of the stone bases, as seen in the excavations. These parameters furthermore accord with the petrological examination of the stones of individual construction areas, matched with their geological sources (e.g., Figure 8). Each workforce team could be composed of few individual laborers. Given the diverse lithological groups that supplied the construction stones ( for loading and unloading in shoulder-mounted supports and/or in bamboo rafts The evident construction units in the walls revealed the products of these small working groups, applied repeatedly for the complete wall construction. Our interdisciplinary research altogether provided a picture of the multiple steps in a massive construction undertaking. Our findings showed that people selected the construction stones from particular natural sources but not from others, in diverse and scattered zones. The episodes of stone collection and transportation could be completed by small teams with flexible arrangements to maximize efficiency. Transportation was the component that required specialized advance planning and coordination to ensure that transportation tools could be available and repaired when needed and other factors. Next, the stones were delivered to designated locations, definitely with preplanning and possibly complicated if multiple construction localities were operating simultaneously. For the final stage of arranging stones into base layers, this task actually was simple in itself, but it involved numerous repeated instances that must have been coordinated toward the overall goal ( Figure 12).
A central organization must have been responsible for coordinating the multiple working groups, producing consistent construction results throughout the wall-building. The organizing efforts would have been necessary for assigning the specific tasks to individuals, creating a workforce schedule, ensuring that everyone followed the plans. Realistically, the project needed to cope with interruptions of severe weather events, floods, and other concerns compounded over time. These aspects about ancient Liangzhu society now can be explored more seriously, for example, following the detailed evidence here about the actual wall construction.

| CONCLUSIONS
The enormous scale of construction at Liangzhu City has prompted an assertion that the planning and logistics behind the construction was so sophisticated that it was critical to the rise of kingship and the emergence of early states (Liu et al., 2017;Liu et al., 2020;Renfrew & Liu, 2018). Our interdisciplinary project contributes new data for this study theme, particularly in terms of the organization and process of the stone collection and construction of the stone bases of the Liangzhu City walls.
For large-scale construction projects at Liangzhu and elsewhere, the full scope of labor activities and contexts cannot be known in their entirety, but the surviving stones hold significant value for revealing the physical outcomes and how those results were possible. The stone components have been well preserved, thus supporting our detailed examinations of their material characteristics, matching with geological sources, and implications of cultural use and labor based on their physical and petrological properties. The interdisciplinary studies described here supported a successful feedback system for a more holistic insight into the stone collection and construction procedures, and their roles in larger contexts of the Liangzhu cultural and natural landscape.

ACKNOWLEDGMENTS
Dr. Michael Carson read previous drafts and provided very useful comments. We also thank the three reviewers and two editors' constructive comments which significantly helped improve the manuscript.

Yijie Zhuang
http://orcid.org/0000-0001-5546-0870 F I G U R E 1 2 Schematic diagram outlining different stages of the production sequence. The question mark refers to two stages (loading and transporting) of the operation that are subject to further investigation [Color figure can be viewed at wileyonlinelibrary.com]