This article outlines the findings of interdisciplinary studies at the three largest medieval fortified settlements (9th-13th centuries AD) on the middle Cheptsa River, northern Udmurtia: Soldyr I Idnakar, Kushman Uchkakar, and Gordino I Guryakar To assess the general trends and characteristic features of their structure and planning, a geophysical survey was carried out, using electrical and magnetic prospecting methods. By correlating geophysical anomalies with excavation findings, two interrelated tasks were completed: reconstructing past events on the basis of archaeological evidence, and assessing the reliability of the geophysical findings. Previously unknown defense lines were revealed at all the sites. Inner layout was virtually linear. Settlement areas (residential, household, and production) were identified. Despite external similarity, the three sites show significant differences in structural and developmental trends. Specifically, at Idnakar and Guryakar, the “annexed” territory protected by a new line of fortifications was used as a household and production periphery. At Uchkakar, this territory was used mainly for residential and household activities, whereas the household and production zone was outside the enclosure. Another distinction of Uchkakar is that the promontory did not reveal the residential, household, or production development zone traditional for Cheptsa settlements. At Guryakar, in contrast to two other sites, an in-depth fortification system was revealed, but no annexed areas.