The Gatehouse is a building found in Pharaoh.
Gatehouses act as a passageway in Walls through which walkers can pass. Simply creating openings in walls defeats the purpose of building walls as enemies can just enter the openings.
Like roadblocks, gatehouses allow destination walkers to pass through, but keep roaming walkers out. Gatehouses do not admit invaders.
Gatehouses are impervious to fire and collapse. They are very negative in terms of desirability.