Defensive improvement. Requires Engineering.
- Constructed on:
A Fort is a special improvement that doesn't increase a hex's productivity or provide access to a resource. Instead, a Fort improves a tile's defensive bonus. Use it to defend choke points in your territory, in regions likely to suffer an enemy invasion. Forts are especially effective when built on hills, because they combine their defensive bonus with the terrain's defensive bonus.
Note that when a unit attacks from a tile with a Fort, it doesn't receive any bonus - the defensive bonus only applies when a unit inside the Fort's tile is attacked.
Fortifications are military constructions or buildings designed for the defense of territories in warfare, and also used to solidify rule in a region during peace time. Humans have constructed defensive works for many thousands of years, in a variety of increasingly complex designs. Most ancient and Medieval Forts were basically improved tall Walls, with some added defensive instruments allowing the defenders to shoot at the attackers, or to pour boiling oil at them.
Roman forts and hill forts were the main antecedents of castles in Europe, which emerged in the 9th century in the Carolingian Empire.
Medieval-style fortifications were largely made obsolete by the arrival of cannons on the 14th century battlefield. Fortifications in the age of black powder evolved into much lower structures with greater use of ditches and earth ramparts that would absorb and disperse the energy of cannon fire. Walls exposed to direct cannon fire were very vulnerable, so they were sunk into ditches fronted by earth slopes.
This placed a heavy emphasis on the geometry of the fortification to allow defensive cannonry interlocking fields of fire to cover all approaches to the lower and thus more vulnerable walls. The star-shaped fort was the most effective design to that end.
The arrival of explosive shells in the 19th century led to yet another stage in the evolution of fortification. Star forts did not fare well against the effects of high explosive and the intricate arrangements of bastions, flanking batteries and the carefully constructed lines of fire for the defending cannon could be rapidly disrupted by explosive shells. Worse, the large open ditches surrounding forts of this type were an integral part of the defensive scheme, as was the covered way at the edge of the counter scarp. The ditch was extremely vulnerable to bombardment with explosive shells.
In response, military engineers evolved the polygonal style of fortification. The ditch became deep and vertically sided, cut directly into the native rock or soil, laid out as a series of straight lines creating the central fortified area that gives this style of fortification its name. Wide enough to be an impassable barrier for attacking troops, but narrow enough to be a difficult target for enemy shellfire, the ditch was swept by fire from defensive blockhouses set in the ditch as well as firing positions cut into the outer face of the ditch itself.
The profile of the fort became very low indeed, surrounded outside the ditch covered by caponiers by a gently sloping open area so as to eliminate possible cover for enemy forces, while the fort itself provided a minimal target for enemy fire. The entrypoint became a sunken gatehouse in the inner face of the ditch, reached by a curving ramp that gave access to the gate via a rolling bridge that could be withdrawn into the gatehouse. Much of the fort moved underground. Deep passages and tunnels now connected the blockhouses and firing points in the ditch to the fort proper, with magazines and machine rooms deep under the surface.
The guns, however, were often mounted in open emplacements and protected only by a parapet; both in order to keep a lower profile and also because experience with guns in closed casemates had seen them put out of action by rubble as their own casemates were collapsed around them. Gone were citadels surrounding towns: forts were to be moved to the outside of the cities some 12 km to keep the enemy at a distance so their artillery could not bombard the city center. From now on a ring of forts were to be built at a spacing that would allow them to effectively cover the intervals between them.
The new forts abandoned the principle of the bastion, which had also been made obsolete by advances in arms. The outline was a much simplified polygon, surrounded by a ditch. These forts, built in masonry and shaped stone, were designed to shelter their garrison against bombardment. One organizing feature of the new system involved the construction of two defensive curtains: an outer line of forts, backed by an inner ring or line at critical points of terrain or junctions (see, for example, Séré de Rivières system in France).
Steel-and-concrete fortifications were common during the 19th and early 20th centuries. However the advances in modern warfare since World War I have made large-scale fortifications obsolete in most situations. Only underground bunkers are still able to provide some protection in modern wars. Many historical fortifications were demolished during the modern age, but a considerable number survive as popular tourist destinations and prominent local landmarks today.