The Fortress At The River, Casbah Ait-Ben-Haddou

Much of the fort moved underground, with deep passages and tunnels to connect the blockhouses and firing points in the ditch to the fort proper, with magazines and machine rooms deep under the surface.
The guns however, were often mounted in open emplacements and protected only by a parapet - both in order to keep a lower profile and also because experience with guns in closed casemates had seen them put out of action by rubble as their own casemates were collapsed around them.
20th and 21st Centuries
Steel-and-concrete fortifications were common during the 19th and early 20th centuries, however the advances in modern warfare since World War I have made large-scale fortifications obsolete in most situations. Only underground bunkers are still able to provide some protection in modern wars. Many historical fortifications were demolished during the modern age, but a considerable number survive as popular tourist destinations and prominent local landmarks today.