A kasbah, also spelled qasba, qasaba, or casbah, is a fortress, most commonly the citadel or fortified quarter of a city. It is also equivalent to the term alcazaba in Spanish, which is derived from the same Arabic word. By extension, the term can also refer to a medina quarter, particularly in Algeria. In various languages, the Arabic word, or local words borrowed from the Arabic word, can also refer to a settlement, a fort, a watchtower, or a blockhouse.

A watchtower or watch tower is a type of fortification used in many parts of the world. It differs from a regular tower in that its primary use is military 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.