noun
camp gate; general's headquarters
Historical military term for the gate of a camp or the presence of a general. In modern Japanese, it is almost exclusively used in the set phrase 軍門に降る (to surrender to an enemy).
敵はついに軍門に降った。
The enemy finally surrendered at the camp gate.
「軍門」は現代では「軍門に降る」という慣用句
In modern times, 軍門 is only used in the idiomatic phrase 軍門に降る.