Terrain Constraint and Visual Relations: A GIS and Null-Model Analysis of Koguryo Fortified Site Siting

The Koguryo kingdom (traditional founding 37 BCE–668 CE) built a broad system of fortified settlements across northeastern Asia’s mountainous regions. Yet, the environmental determinants of their locations remain underexplored in quantitative terms. This study applies GIS-based terrain analysis and a Monte Carlo null model to 41 verified Koguryo fortified sites. The results reveal a corridor-mediated distribution shaped by terrain: 90.2% of sites lie on slopes ≥ 10° and 65.9% within 1 km of a perennial river, while 66.8% of site pairs are separated by >100 km, a statistic that partly reflects the broad study region; the dual-scale nearest-neighbor analysis and the KDE–river coincidence support terrain-mediated dispersal along valley corridors. An intervisibility null-model analysis finds minimal mutual visibility (3 reciprocal pairs, 0.37%; 23 one-way pairs, 2.80%), not significantly different from random resampling within the terrain envelope (N = 999, p = 0.419), a result consistent with visibility not having been a primary locational factor. Historical records of construction-technique transmission are qualitatively consistent with inter-polity exchange, although this dimension is not quantified here. The study offers a transferable methodology linking terrain characterization with a visual null model, advancing landscape-archaeological understanding of settlement–environment interaction.