Fortification
Fortifications are military constructions designed for defensive warfare. They have been used for many thousands of years, in a variety of increasingly complex designs. The practice of improving an area's defense is also known as "fortification". Many military installations are known as forts, although they are not always "fortified".
See also: castle, city wall, Medieval fortification, pillbox[?], siege warfare[?], stockade[?]
List of fortifications
List of forts