When a civilization has learned construction, its workers know how to construct stone and masonry barricades, which are even more formidable than Fortresses. A Barricades can only be built on a square already containing a Fortress. Even if unoccupied, barricades automatically stops movement of a ground unit entering its square (unless that unit belongs to the same civilization currently controlling the barricade's square, or if that unit has a Right of Passage agreement through that land. Barricades become a fortress if their square is pillaged. Military units inside barricades have a few advantages. * They get a 100% defensive bonus if attacked (i.e., twice the defensive bonus being in a Fortress). * The zone of control exerted by the fortress still applies to a barricades.