In the early days, it was usually a temporary structure for defensive and watching purposes to hold a castle in wartime, as seen in medieval illustrated scrolls, such as "Gosannen Kassen Ekotoba (A Scroll of the Late Three Years War)" and "Ippen Shonin Eden (Pictorial Biography of the Monk Ippen)."
初期の頃は、『後三年合戦絵詞』や『一遍上人絵伝』など中世の絵巻物に見られるように、篭城戦での防御・物見のための仮設の建造物としての要素が強かった。