<p>Fort settlements, a type of defensive settlement, represent significant historical heritage in China. Taking fort settlements in the Fen River Basin of China as a case study, this research reveals their site selection characteristics from both a whole-entity perspective and an individual-level perspective, and explores the correlations between geographic parameters and defense patterns. Surface roughness was employed to quantify terrain complexity, while the multifractal method from fractal theory characterized slope gradients and river system distributions. The results indicate that the site selection of fort settlements was predominantly influenced by the convenience of production and daily life, with micro-location adaptation, while different geographical conditions shaped their defensive patterns. This study offers a multi-scale and parameterized technical framework for exploring the mechanisms of historical settlement site selection.</p>