Each corner of the square shaped Honmaru area was pointing to the four points of the compass, and the watchtowers at each corner were named after the directions: Ushitora yagura, Tatsumi yagura, Hitsujisaru yagura, Inui yagura.
ほぼ東西南北の正方形構造なので、その矢倉には方角にちなみ艮矢倉、巽矢倉、坤矢倉、乾矢倉の名である。