Star fort
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A Star Fort is a fortification in the style that evolved during the "Age of Blackpowder" when the cannon came to dominate the battlefield. Passive fortifications of the medieval era proved vulnerable to reduction by cannonfire.
The response from military engineers was to arrange for the walls to be embedded into ditches fronted by earth slopes so that they could not be attacked by direct fire, which is by far the most destructive, and to have the walls topped by earth banks that absorbed and largely dissipated the energy of plunging fire. Where conditions allow, as in Fort Manoel in Malta, the "ditches" are cut into the native rock, and the "wall" at the inside of the ditch is simply unquarried native rock.
The ditches and walls channel attacking troops into carefully constructed killing grounds where defensive cannon can wreak havoc on troops attempting to storm the walls, with emplacements set so that the attacking troops have no place to shelter from the defensive fire.
A further and more subtle change was to move from a passive model of defence to an active one. The lower walls were more vulnerable to being stormed, and the protection that the earth banking provided against direct fire failed if the attackers could occupy the slope on the outside of the ditch, and mount attacking cannon there.
Thus forts evolved complex shapes that allowed defensive batteries of cannon to command interlocking fields of fire. Forward batteries commanded the slopes which defended walls deeper in the complex from direct fire. The defending cannon were not simply intended to deal with attempts to storm the walls, but to actively challenge attacking cannon, and deny them approach close enough to the fort to engage in direct fire against the vulnerable walls.
The key to the forts defense moved to the outer edge of the ditch surrounding the fort, known as the covered way, or covert way. Defenders could move relatively safely in the cover of the ditch, and could engage in active counter measures to keep control of the glasis, the open slope that lay outside the ditch, by creating defensive earthworks to deny the enemy access to the glasis and thus to firing points that could bear directly on to the walls, and by digging counter mines to intercept and disrupt attempts to mine the fort walls.
Compared to medieval fortifications, forts became both lower and larger in area, providing defence in depth, with tiers of defences that an attacker needed to overcome in order to bring cannon to bear on the inner layers of defences.
Firing emplacements for defending cannon were heavily defended from bombardment by external fire, but open towards the inside of the fort, both to diminish their usefulness to the attacker should they be overcome, but also to allow the large volumes of smoke that the defending cannon would generate to dissipate.
Fortifications of this type continued to be effective while the attackers were armed only with cannon, where the majority of the damage inflicted is caused by momentum from the impact of solid shot. While only low explosives such as blackpowder were available, explosive shells were largely ineffective against such fortifications.
The development of high explosives, and the consequent large increase in the destructive power of explosive shells and thus plunging fire rendered the intricate geometry of such fortifications irrelevant.
External links
- [Star fort pictures and drawings]
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