Written sources of the 17th century mention “kosoi” (angular or slanted) forts. F.F. Laskovsky of the Engineer Corps interpreted this term as referring to forts with walls made from inclined logs (palisades). This idea was generally accepted by the scholarly community. The architect S.N. Balandin, without offering any proof, claimed that the “kozelchaty” forts (from “kozly”, trestle supports) were a subtype of “kosoi” (angular) forts. The purpose of the present study is to test the conclusions of Laskovsky and Balandin using new evidence. As it turns out, neither the written nor archaeological sources support these versions. In fact, there is enough information to disprove both. The meaning of the word “kosoi” in the 17th–19th century Russian language suggests four hypotheses regarding the structure of walls of “angular” forts. Comparison of them reveals that the term “angular” referred to fortifications with nonstraight walls, those joining not at a right angle, as well as those that were triangular in plan view. The specific layout of “kozelchaty” forts cannot be determined due to the lack of evidence. Probably their walls actually rested on trestle supports—two supports made of two or three logs each, on which a horizontal log was placed. Such forts were common mostly in northeast Asia, where forests were scarce, and the ground was frozen or rocky, preventing people from digging ditches for log palisade walls.