Human struggled against floods and wars in mountain-gorge of NE Tibetan Plateau: unique city-wall system evidence

Flooding and warfare were important challenges to the development of human societies in the Late Holocene, especially in flood-prone areas, including the Bailongjiang Basin in the northeastern Tibetan Plateau. It is not clear how ancient societies in this region fought against flooding and war, and its study is an important way to explore the patterns of human-environment interactions. In response to these questions, a detailed survey of ancient cities in the upper Bailongjiang River during the historical period was carried out, and 42 dating samples were collected from six ancient cities and one site. The results showed that these ancient cities were mainly built during the Tang and Qing dynasties. Among them, a unique three-dimensional defence system was discovered for the first time in the investigation and research in the area of the ancient city of Diezhou, including city walls and water retaining walls from the Sui and Tang dynasties, as well as enclosure walls and beacon flints from the Qing dynasty. A combination of geomorphological surveys, historical documents, and paleoclimatic data suggests that ancient humans constructed the three-dimensional defence system in this area mainly in response to high-frequency flooding triggered by climate change, as well as wars between the Tang and Tubo, and between the Qing and the Heshuit Khanates. This study provides a typical example of human-water-war interactions during the historical period in the high mountain valley area of the northeastern Tibetan Plateau, which is of great academic value for the in-depth understanding of the process and mechanism of the evolution of human-earth relations in the high mountain valley area.