So I recently tried to fight as the Roman faction and noticed something when I tried to build the fortified siege camp & siege walls and towers. They all decay back to Gaia. Now, this is not so much a problem HOWEVER. The gatehouse cannot be garrisoned and thus eventually will be lost to either the enemy or to Gaia. So! Either make the gate house garrisonable or remove decay for gatehouses because using siege gatehouses right now is out of the question.