Subsistence strategies and climate change as key factors in the vicinity of the Great Wall in northern China from 500 BCE

Whether, and in what ways, the association between changes in climate and the shifting of imperial frontiers (i.e. the Great Wall) could be mediated by the social responses of major ethnic groups is a question that remains unanswered. Ulanqab is a region in Inner Mongolia associated with a long history of Great Wall construction from the Warring States to the Ming dynasties (~500 BCE–1644 CE) and the Great Wall is often regarded as the boundary of the Central Plains dynasty. This paper uses Ulanqab as a case study to investigate the historical inter-relationship between changes in climate and subsistence strategies on the one hand, and the positioning of the Great Wall on the other. We determined the precise geographical coordinates of the Great Wall in this region during each dynastic period of Chinese history, and compared its location to (1) the empire’s boundaries in each dynasty, (2) evidence that is available on climate change from high-resolution paleo-climate reconstructions and (3) subsistence strategies (whether agriculture, pastoralism, or nomadism) that people adopted as recorded in historical documents. Geo-referenced information from associated archaeological sites was also used to determine the extent of habitation in different areas. We found that during the period of agriculturalist empires (the Han and Ming dynasties), the Great Wall was a frontier between farming and animal husbandry, and was located to the south of the Daqing Mountains. In contrast, during the period of pastoralist empires (the Zhao Kingdom [of the Warring States], Northern Wei and Jurched Jin periods), the Great Wall was the frontier between animal husbandry and nomadism, and was located to the north of the Daqing Mountains. These mountains (42.5°N) seem to have been the northern limit of human settlements that were based on animal husbandry and farming. We observed that, when precipitation and temperature increased, this resulted in an augmentation of agricultural production that most likely facilitated the northward expansion of the agriculturalist peoples. A decrease in precipitation, on the other hand, resulted in the shrinkage of pastures and food, triggering a southward expansion that was characteristic of the pastoralist peoples. This study attempts to provide new insights into the interrelationships among changes in climate, human societies and geopolitics in Chinese history.