An Oten-mon Gate (応天門 or 應天門.) was located on the back side of the palace of the Heijo-kyo Capital and another Oten-mon Gate on the back side of the palace of the Heian-kyo Capital: The Oten-mon Gate constituted the official gate to Chodoin (Hasshoin) where government operations and important ceremonies in the Imperial Court were executed.
応天門（おうてんもん、應天門）は、平城京、平安京大内裏にあった門で、朝廷内での政務・重要な儀式を行う場であった朝堂院（八省院）の正門であった。