Since Warlords, every civilization in Civilization IV has had their own unique building. A unique building, or UB for short, is a building that can only be built by that civilization. It always replaces some other building, not allowing that one to be built at all.
|Civilization IV |
|Warlords • Beyond the Sword • Colonization†|
|† Total conversion remake of the game Sid Meier's Colonization using Civilization IV engine|