Ō -mon, the biggest gate in Naegi Castle is a two-storied structure, separating San-no-maru (outermost region of the castle) and Ni-no-maru (outer citadel). The gate is about 5 m (16.4 ft) wide. The second floor was used as a storage. The gate was kept closed all the time except for occasional major events such as departure of the lord for Edo for Sankin-kotai (an alternate-year attendance). Normally, the side gate was used instead.