Gatehouse

Grand enough to welcome guests, sturdy enough not to.

The way through a wall. It lets your side and your allies pass, and shuts when anyone else comes within 5 tiles: enemy troops and workers, and bandits. It opens again half an hour after the last of them is more than 7 tiles away.

Only the passage shuts. The stairs up to the wall walk stay open, so a gatehouse is also how your troops get onto the wall.

The game’s own Closed and Automated gate modes still work, so a Watchtower’s automation signal can close it before anyone gets near.

A Battering Ram is the machine for breaking one.