Site Selection and Defensive Spatial Organization of Ming–Qing Tusi Settlements in the Gyalrong Tibetan Region of China

Tusi settlements in the Gyalrong Tibetan region of China developed within complex high-mountain gorge environments, where settlement construction, territorial control, and military defense were closely intertwined. However, existing studies have largely examined individual Tusi manors, watchtowers, or geographical settings in isolation, leaving the relationships between environmental conditions, site selection, and defensive spatial organization insufficiently understood. To address this gap, this study develops an integrated multiscale analytical framework linking regional environmental context, local terrain selection, and settlement defensive spatial organization. Drawing on a historical and geographical database of 58 Tusi settlements from the Ming and Qing dynasties and detailed spatial investigations of 12 cases, this study combines regional environmental clustering, neighborhood-based terrain comparisons, and defensive-element mapping to examine how these three spatial levels are related. The results identify four regional site-selection types reflecting differentiated combinations of elevation, slope, and river proximity. Despite these environmental differences, 63.8% of the settlements occupy locally less rugged and gentler terrain, while 62.1% are situated in areas characterized by relatively high flow accumulation. These findings indicate that settlement locations generally balanced construction suitability with access to surrounding terrain features that could provide defensive advantages. At the settlement scale, four major defensive spatial patterns were identified in relation to site-selection environments, revealing how Tusi manors, watchtowers, access routes, and natural barriers were spatially integrated under different topographic conditions. The central finding is that defensive spatial organization did not rely solely on occupying strategically elevated terrain or constructing isolated fortifications, but emerged from the spatial integration of relatively suitable settlement cores, surrounding terrain barriers, and strategically positioned defensive elements. By connecting regional environmental constraints with local siting decisions and settlement-scale spatial organization, this study provides an integrated explanation of the defensive landscapes of Gyalrong Tusi settlements and a spatial basis for their holistic conservation.