Fortifications are military constructions and buildings designed for defense in warfare and military bases. Humans have constructed defensive works for many thousands of years, in a variety of increasingly complex designs. The term is derived from the Latin fortis ("strong") and facere ("to make").

Nomenclature

Many military installations are known as forts, although they are not always fortified. Larger forts may class as fortresses, smaller ones formerly often bore the name of fortalices. The word fortification can also refer to the practice of improving an area's defense with defensive works. City walls are fortifications but not necessarily called fortresses.

The art of setting out a military camp or constructing a fortification traditionally classifies as castrametation, since the time of the Roman legions. The art/science of laying siege to a fortification and of destroying it has the popular name of siegecraft or 'siege warfare' and the formal name of poliorcetics. In some texts this latter term also applies to the art of building a fortification.

Fortification is usually divided into two branches, namely permanent fortification and field fortification. Permanent fortifications are erected at leisure, with all the resources that a state can supply of constructive and mechanical skill, and are built of enduring materials. Field fortifications are extemporized by troops in the field, perhaps assisted by such local labor and tools as may be procurable and with materials that do not require much preparation, such as earth, brushwood and light timber, or sandbags (see sangar). There is also an intermediate branch known as semipermanent fortification. This is employed when in the course of a campaign it becomes desirable to protect some locality with the best imitation of permanent defences that can be made in a short time, ample resources and skilled civilian labor being available.

Castles are fortifications which are regarded as being distinct from the generic fort or fortress in that it describes a residence of a monarch or noble and commands a specific defensive territory.

Ancient

From very early history to modern times, walls have been a near necessity for every city. Uruk in ancient Sumer (Mesopotamia) is one of the world's oldest known walled cities. Before that, the city (or rather proto-city) of Jericho in what is now the West Bank had a wall surrounding it as early as the 8th millennium BC.

The Assyrians deployed large labour forces to build new palaces, temples and defensive walls.
Some settlements in the Indus Valley Civilization were also fortified. By about 3500 B.C., hundreds of small farming villages dotted the Indus floodplain. Many of these settlements had fortifications and planned streets. The stone and mud brick houses of Kot Diji were clustered behind massive stone flood dykes and defensive walls, for neighboring communities quarreled constantly about the control of prime agricultural land. Mundigak (c. 2500 B.C.) in present day south-east Afghanistan has defensive walls and square bastions of sun dried bricks.