Hill-forts are hills, capes of river valleys adapted to defence. They have flat plateaus on the top, slopes made steeper by defenders and defensive arrangements. Wooden castles used to stand on them. The earliest hill-forts appeared in the territory of Lithuania at the turn of the 2nd - 1st millennium B.C. Wooden castles formed defence lines during formation of the state of Lithuania and the wars against Crusaders in the XII-XV centuries. Wooden castles lost their defensive importance after Grunwald and Pabaiskas battles.