The article deals with the history of development of the Old Russian defensive architecture after Mongolian invasion: in the second half of the 13^th — mid 14^th century. The construction of stone fortresses at this time was sporadic. Two main traditions can be distinguished, one of which is characteristic for Western Rus’, and the other for North-Western Rus’. Most likely, the earliest fortifications of Western Rus’ were wood-earthen walls, with individual stone defensive towers within the ring. In North-Western Rus’, at the end of the 13^th century, we can find irregular fortresses with stone walls, but apparently without towers. Fortifications with a fairly clear, almost regular plan (Orlets, Oreshek) appeared in the 1340—1350s. The middle of the 14^th century seems to be a new turning point in the development of ancient Russian fortification.