A watchtower or guardtower (also spelt watch tower, guard tower) is a type of military/paramilitary or policiary tower used for guarding an area. Sometimes fortified, and armed with heavy weaponry, especially historically, the structures are built in areas of established control. These include military bases, cities occupied by military forces, prisons and more. A common equipment is searchlights.
It differs from a regular tower in that its primary use is military/policiary and from a turret in that it is usually a freestanding structure. Its main purpose is to provide a high, safe place from which a sentinel or guard may observe the surrounding area. In some cases, non-military towers, such as religious towers, may also be used as watchtowers.
Similar constructions include: observation towers, which are generally civilian structures, and control towers, used on airports or harbours.