Tenshu, the Boro part of which was constructed small with high rate of decrease in roof size, are regarded as early period ones, including the Tenshu of Inuyama-jo Castle and Maruoka-jo Castle, which are understood to have been constructed before the Battle of Sekigahara.
関ヶ原の戦い以前に造られたとされる犬山城や丸岡城の天守など、屋根の逓減率が大きく、望楼部分が小さく造られているものを初期という。