Historic evolution
The history of silo-caves dates back all the way to the early Neolithic Age. Ancient residents living in the loess area and transferring from drifting around to settling down built their homes by caving the loess ground, which was highly adapted to the local condition [24–25]. Such underground cave and semi-underground cave dwellings were found in the Peiliguang ancient cultural relic dating back to 9000–7000 years ago, specifically in both the Egoubeigang relic of Xinmi [26] and the Tanghu relic of Tanghu, Henan [27]. Such dwellings are small in size, with areas generally below 10 m2 and depth below ground level of 0.5–1 m. Without doubt, these underground cave and semi-underground cave dwellings are the embryo form of the later silo-cave, and further demonstrate the time-honored history and environment-adapted tradition of building homes of residents in the loess area by excavating the loess ground
In the late stage of the Yangshao culture about 5000 years ago, true cave dwellings occurred in the loess area. The oldest cave-dwelling architecture discovered so far is located in the Yanggu relic of the late Yangshao culture, Ning County, Gansu Province [28]. The subsequent Longshan culture (5000–4000 years ago) is seen with increasing cave-dwelling architecture, which gradually evolve into an important dwelling form for early human beings in the loess area. During this process, various styles of cave-dwelling architecture emerged, and the earliest silo-cave architecture came into being—a cave dwelling with a vertically-excavated vestibule. The cave dwelling itself is excavated on the wall of the vestibule. Such cave-dwelling remains were found in both the Taosi [29] and Dongxiafeng [30] relics. Later in the Bronze Age (4000–3000 years ago), this form of cave-dwelling architecture became very popular in the loess area [31].
During the Qin and Han dynasties (2000 years ago), the masonry-timber structure gradually replaced the earth-timber structure and emerged as the main house form in China at that time. However, due to the traditional culture and economic limitation of the economy, cave dwellings remained an important dwelling form for residents in the loess area [32]. Cave-dwelling architecture that shared similarities in shapes and structures with the model silo-cave occurred during this period. A U-shaped tomb of the Han dynasty was found in Sanmenxia, and features multiple tomb caves distributed on the three sides of the tomb. The overall tomb structure resembles a complete courtyard, and looks (from above) extremely similar to the modern “silo-cave”.
From the late stage of ancient Chinese history to the modern times, silo-caves became the most primary dwelling form in some areas of loess terrace-like plains. This phenomenon continued until the period of reform and opening up of China, after which residents in loess terrace-like plains gradually moved to the ground and lived in above-ground buildings, with the improved economy and change in the concept of dwelling. Moreover, due to the implementation of land reclamation, numerous silo-caves were abandoned and backfilled, which results in the rapidly reduced quantity of silo-caves. People have gradually been re-aware of the uniqueness and scarcity of silo-caves since the 1990s. Then, some areas started to protect silo-caves or convert them into tourist sites, which marked a new period for the exploitation of silo-caves (Fig. 2).
Spatial distribution framework
Remote sensing interpretation reveals that traditional silo-cave villages are mainly located in the terrace-like plain area of the Loess Plateau in North China, featuring thick soil layers and arid climate. The primary concentration of silo-cave villages is found in the Yuxi-Jinnan (West Henan-South Shanxi) and Guanzhong-Longdong (Central Shaanxi-East Gansu) areas (Fig. 3). Silo-caves in the Yuxi-Jinnan area are mainly located at the central zones along mountains or the Yellow River, presenting the loess terrace-like plain landform. Specifically, the Yuxi silo-cave is mostly located at the loess terrace-like plain of the eastern margin of the Loess Plateau, such as Gongyi City, Xinan County, Shanzhou District, and Lingbao City. The loess tableland area in the southwestern Shanzhou District, Sanmenxia City owns silo-caves with the largest scale and most concentrated distribution among existing silo-caves in China, mainly in towns such as Zhangbian, Xizhangcun, and Caiyuan. Incomplete statistics show that there are still over 100 below-ground traditional villages composed of nearly ten thousand silo-caves. It should be noted that before 1980, the silo-cave dwelling is the only dwelling form in the loess tableland area of Shanzhou District. The Jinnan silo-caves are primarily built in the loess terrace-like plain area between the Zhongtiao Mountain and Yellow River, and the main concentration is seen in the towns of the mid-western Pinglu County (e.g. Zhangdian and Changle). As for the silo-caves in the Guanzhong-Longdong area, they are concentrated at the loess terrace-like plain area of the valley of the Jinghe River. Moreover, the Guanzhong silo-caves are mainly distributed in the arid Weibei plain of the transition zone from the Weihe Basin to the Loess Plateau, e.g. the counties such as Changwu, Binzhou, Xunyi, Chunhua, Yongshou, Qianxian, Liquan, and Sanyuan of Xianyang City, Shaanxi Province. On the other hand, Longdong silo-caves accumulate at Dongzhi Tableland in the mid-eastern Qingyang, Gansu Province. From north to south these silo-caves concentrate at Qingcheng County, Heshui County, Qingyang City, and Ningxian County, where they spread outward from the central area of the county across the flat tableland surface. The main concentration is found in Qingyang City and its surrounding areas, followed by the areas along main roads. Areas near the river valley and gully are also seen with numerous silo-caves.
The areas with the concentrated distribution of traditional silo-cave villages are located in the central Loess Plateau and share distinctive regional natural conditions, in terms of the landform, climate, soil, etc. Meanwhile, these areas are all economically underdeveloped and classified as the traditional agricultural regions. Close geographical relationships and consistent cultural settings are found between these areas. Thus notable patterns can be found with respect to the spatial distribution framework of the silo-cave village.
Similar landforms
The distribution areas of silo-caves all present the landforms of the loess tableland and terrace-like plain of the Loess Plateau, which are mainly characterized by a flat and wide top platform extending downward smoothly and slowly along the hill. The slope of the top platform is mostly of 1–3° and can reach 5° at the platform edge. The surrounding of the top platform is cut off by gullies. Due to such landforms featuring localized flatness, ancient residents living there had no cliffs and gully walls to build caves. Therefore, they innovatively constructed cave dwellings penetrating into the underground to create a relatively comfortable, wind-proof, and warm-keeping environment for living. This led to occurences and development of silo-caves in these areas.Fig. 3 Distribution of traditional silo-cave villages in the middle reaches of the Yellow River: (1) Yuxi-Jinnan;( 2) Guanzhong-Longdong
Similar Climates
The Yuxi-Jinnan and Guanzhong-Longdong areas are both mid-altitude inland areas, and they are featured by the warm temperate continental monsoon climate. The four seasons are distinctive in these areas. Spring is dry and windy; summer is hot and rainy; the temperature drops rapidly in autumn; winter is cold and yet rarely snowy. Rainfall is concentrated in July–September, and the annual average temperature is 9–14°C. To sum up, the climate there is characterized by hot summer and cold winter, drought, limited rainfall, relatively strong wind with entrained sands, and intensive sunlight. Due to such climate features, people living there try to use the dwelling design to offset the disadvantage of natural conditions—the silo-cave architecture hides beneath the ground, with the overlying formation to facilitate the indoor environment warm in winter and cool in summer, the advantage of “cave dwelling”. The room temperature can maintain above 11°C in winter and below 20°C in summer. Furthermore, the small downward-excavated courtyard of the silo-cave can effectively avoid strong wind and therefore dust, and de-noise, to create an environment applicable to human dwelling and food storage. Clearly, the silo-cave serves as a protective shield between humans and the harsh natural climate condition.
Analogous soil conditions
These areas are endowed with abundance in loess. The loess deposit is thick, with a thickness generally of 20–250 m. Loess there are deposited during the early, middle, and late Pleistocene. The loess layer is rigid, tight, and commonly developed with vertical joints (therefore high capacity to maintain the standing posture and less prone to collapse). It is resistant to vertical loading, earthquake, and alkaline corrosion. Moreover, the arid climate there is in favor of soils to keep dry and rigid, which improves the service life of cave-dwelling architecture. The natural conditions of areas with concentrated distributions of silo-caves are summarized in Table 1.
Table 1
Natural conditions of areas with concentrated distributions of silo-caves
Area
|
Landform
|
Elevation / m
|
Climate
|
Annual Average Precipitation / mm
|
Annual Temperature / °C
|
Soil Thickness / m
|
Yuxi
|
Loess terrace-like plain at the eastern margin of the Loess Plateau
|
500–800
|
Warm temperature monsoon climate
|
550–680
|
13.6
|
20–70
|
Jinnan
|
Loess terrace-like plain between the Zhongtiao Mountain and Yellow River
|
500–700
|
Warm temperature monsoon climate
|
500–620
|
13.8
|
40–50
|
Guanzhong
|
Loess terrace-like plain of Guanzhong
|
400–600
|
Warm temperature monsoon climate
|
600–700
|
13.3
|
80–100
|
Longdong
|
Loess terrace-like plain of the Shan-Gan-Ning Basin (Dongzhiyuan)
|
1250–1400
|
Warm temperature monsoon climate
|
480–550
|
9.1
|
150–250
|
Homogeneous economic levels and structures
The silo-cave concentration areas are all economically-underdeveloped areas of Middle and West China. In these areas, the backward economy suffers from an inferior economic foundation. The regional economy is mainly based on conventional agriculture, which leads to a simple economic structure. Taking Shanzhou District in the Yuxi area, Pinglu County in Jinnan, Chunhua County in Guanzhong, and Qingcheng County in Longdong as examples, the per capita gross domestic production (GDP) and rural per capita disposable income in 1978, 2008, and 2018 are all below the national average levels (Table 2 and Fig. 4). In the early stage, these areas are commonly seen with a lack of construction materials to build dwellings, and people living in such wide plains with insufficient natural barriers and construction materials have to seek shelter in the underground space. Therefore, the choice is made to excavate the ground and build homes, which gradually evolves into a dwelling habit during the prolonged history that continues up to now.
Table 2
Economic levels of areas of traditional silo-cave villages in 1978–2018
Term
Area
|
Per Capita GDP
/ RMB Yuan
|
Rural Per Capita Disposable Income
/ RMB Yuan
|
1978
|
2008
|
2018
|
1978
|
2008
|
2018
|
Shanzhou, Henan
|
324
|
18484
|
45855
|
126
|
4192
|
12916
|
Pinglu, Shanxi
|
211
|
5986
|
18164
|
101
|
2777
|
7776
|
Chunhua, Shaanxi
|
265
|
10438
|
35689
|
119
|
2946
|
9721
|
Qingcheng, Gansu
|
245
|
11973
|
38952
|
102
|
2696
|
8595
|
Nation-wide average
|
381
|
22698
|
64644
|
134
|
4761
|
14617
|
Consistent cultural settings
The Chinese Civilization originated from the hinterland in the middle reaches of the Yellow River, which, as the source of the ancient civilization of the Yellow River valley, provides a consistent cultural setting for people across the area. Due to the close geographic relationship and consistent cultural setting, people living in the silo-cave concentration areas have similar dwelling forms and habits. Discoveries in base sites of numerous relics of the Yangshao culture in these areas, such as the Miaodigou relic in Shanzhou District, Beishouling relic in Baoji, Jiangzhai relic in Lintong, Banpo relic in Xi’an, Xiwangcun relic in Ruicheng of Shanxi, have shown that the village dwellings in this historic period are dominated by semi-underground caves. Owing to the dry climate and thick soil layers of the Loess Plateau, ease in excavation, and the advantage in the lee of keeping warm and effectively avoiding winds (and entrained sands), cave dwelling and semi-cave dwelling architecture extensively occurred and developed in these areas. As time passed by, cave dwellings evolved from horizontal caves, to bag-like vertical caves, then semi-cave dwellings, and at last the present silo-cave architecture. Clearly, the consistent cultural setting contributes to the occurrence, development, and inheritance of traditional silo-cave villages in the areas mentioned above.
Morphological evolution characteristics of typical villages
Morphological evolution patterns of typical villages
By analyzing the morphological evolution of typical silo-cave villages since 1980, such as Houguan and Miaoshang Villages of Xizhangcun Town, and Qucun Village of Zhangbian Town in Shanzhou District, this paper managed to identify three patterns of morphological evolution of traditional silo-cave villages, namely retaining the periphery and rebuilding the interior, retaining the interior and expanding the periphery, and expanding both the periphery and interior.
(1) Retaining the periphery and rebuilding the interior
Houguan Village is located in Xizhangcun Town, Shanzhou District, with the Dalei line of the provincial highway S245 penetrating the center of the village. Before 1980, villagers mostly lived in silo-caves. Since 2000, above-ground dwellings were built mainly along the provincial highway S245. By 2018, more above-ground buildings have been placed inside the village along the main traffic roads, which leaves only the periphery of the village retaining some traditional silo-cave architecture (Fig. 5). The silo-cave settlement morphology of the whole village presents the unchanged periphery and rebuilt interior, in which the traditional silo-cave villages are abandoned and newly-built above-ground buildings are placed along main roads inside the original village. Factors contributing to such evolution of traditional villages include traffic, administrative policy, and self-agency of villagers, among which variation of traffic conditions and resultant guiding effects are the main contributors.
(2) Retaining the interior and expanding the periphery
Miaoshang Village is located in Xizhangcun Town, Shanzhou District, Henan Province. The remote sensing imaging in 1980, 2000, and 2018 reveals a pattern of retaining the interior and expanding the periphery, in terms of the morphological evolution of the whole village (Fig. 6). With this pattern, the traditional silo-cave village is generally well preserved, and new buildings for the village are built in the periphery of the original village in a well-planned manner. Factors leading to this pattern of traditional village evolution are the administrative policy, planning guidance, and self-agency of villagers, among which the administrative policy and planning have significant impacts upon the morphological evolution of villages.
(3) Expanding both the periphery and interior of the village
Qucun Village is located in Zhangbian Town, also Shanzhou District, Henan. It is seen in the remote sensing imaging of 1980, 2000, and 2018 that the morphological evolution of the whole village is characterized by the expansion of both the interior and periphery of the village. Newly-built above-ground buildings are randomly placed both in the interior and on the periphery of the original village (Fig. 7). In this evolution pattern, the traditional silo-cave village is generally found with the simultaneous hollowing and periphery expansion, and the style and spatial texture of the previous traditional silo-cave village are compromised. Factors affecting this traditional village evolution pattern are mainly the self-agency of villagers, traffic infrastructure, and government guidance, among which lack or delaying of administrative policy and planning is the major contributor.
Evolution regularity of internal structures of typical traditional villages
Here Qucun is further analyzed to demonstrate the spatial structure evolution characteristics of internal structures (including both silo-caves and above-ground buildings) of the village at different time moments. Two time moments, namely 1969 and 2018, are chosen for analysis.
Qucun, a typical traditional silo-cave village, features a landform of the typical loess tableland at the eastern margin of the Loess Plateau. In September 2016, Qucun was included in the 4th List of Traditional Villages of Henan Province. In 2018, the total village area of Qucun reaches 287 hectares, among which 40.75 hectares are of village construction; 152.67 hectares, of farming; 66.54 hectares, of woods; 27.04 hectares, of other usages. There are now ten villager groups in Qucun, including a total of 435 households for a total population of 1527.
Remote sensing interpretation illustrates 172 silo-cave settlements across the village in 1969 (Fig. 8a). Over recent years, the quantity of silo-caves in Qucun gradually declines. According to field survey and document review, there were 130 silo-cave settlements in Qucun in 2018, presenting a reduction by 42 from 1969. The existing silo-caves were mostly built before 1949, among which two were built in the Ming dynasty; 32, in the Qing dynasty; 49, during the period of the Republic of China. Forty-seven silo-caves were built after 1949. Among the existing silo-caves, 74 (57% of the total) are well preserved, with structural integrity and retained style and features. Twenty-one silo-caves (16% of the total) are seen with slight inferior preservation, with partial structures and decorative elements damaged. The rest 35 silo-caves (27% of the total) are found with remaining overall structures and yet collapse of caves on one or more sides of the courtyard. Moreover, numerous above-ground dwellings have been built (Fig. 8c), including a total of 20 households with brick houses, mostly constructed before 2010, and 110 households with storied and one-story houses, mostly built after 2010. The silo-caves and above-ground architectures are arranged in a chaotic manner, which damages the morphology and texture of the original village. The building distribution inside the traditional silo-cave village is vectorized via interpretation and digitization of the remote sensing image (Figs. 8b and 8d).
Then, with the Density tool in the ToolBox of ArcGIS 10.1, the kernel density analysis has been carried out on the settlements of Qucun in 1969 and 2018 (Fig. 9). By doing so, agglomeration of traditional in this traditional village was investigated at the micro-scale, which mainly produces the following findings:
(1) There are mainly four agglomeration zones of silo-caves in Qucun, located in the northeastern, northern, central, and southwestern parts of the village, respectively (Fig. 9a).
(2) Compared with 1969, 2018 presents a huge reduction of the silo-cave quantity, mostly occurring in the central and southern parts of the village. The existing silo-caves are concentrated in three zones, located in the northeastern, northern, and southwestern parts of the village (Fig. 9b).
(3) Distribution of newly-built above-ground architectures is less organized. Such architecture is randomly placed inside the village, and the two zones with relative concentrations of them are in the northwestern and southeastern parts of the village (Fig. 9c).
Based on analysis of the morphological evolution characteristics and variation of settlement agglomeration of Qucun, a typical traditional silo-cave village, we managed to carry out further function division of this traditional village, in accordance with the consistency of the overall village landscape spatial texture. The key protection zone for silo-caves is demarcated, and some modern above-ground buildings that are inconsistent with the traditional style and features of the village are removed or relocated, which provides technical support to developing the concept of renovating the internal structure of the traditional silo-cave structure (Fig. 10).