The article discusses about reasons for the emergence of tradition to build multiple ramparts to the hillforts. The authors offer their own fundamentally new view and criticize existing concepts. The research based both archival materials and field study in 2019–2020. Application of method by A.V. Korobeinikov the simulation modeling by archaeology data, made it possible to reveal the logic and the algorithm of building the fortifications to the hillforts of the 1^st millennium AD. In the paper the foundations of the theory of fortification are presented, as applied to archaeology. An algorithm the transformation of fortifications on hillforts of the 1^st millennium AD has been shown from simple to more complex. Information about a series of hillforts in the Perm region have been involved into the scientific discurs. Including, specificities of the geomorphology and hydrology of the location of hillforts with multiple ramparts and their link with ore deposits (copper sandstone and sederite) were revealed.