A structurally reinforced defensive building constructed during the Second World War at strategic locations, primarily to stop invasion forces. There were initially seven basic designs, though modification and even single types were not unusual. Various types of camouflage were also common. Most pillboxes were roughly circular or rectangular in design, built of concrete and intended to house infantry and rifle or light machine gun emplacements. Specific features included slits through which the guns were fired and blast walls to protect the entrance.