Everything about Star Fort totally explained
A
star fort or
trace italienne is a
fortification in the style that evolved during the age of
black powder, when
cannon came to dominate the
battlefield, and was first seen mid-15th century in
Italy. Passive ring-shaped (
enceinte)
fortifications of the medieval era proved vulnerable to damage or destruction by cannon-fire, when it could be directed from outside against a perpendicular masonry wall. In contrast, the star fortress was a very flat structure composed of many triangular
bastions, specifically designed to cover each other, and a ditch. Further structures such as
ravelins,
hornworks or
crownworks, and detached forts could be added to create a complex symmetrical structure.
Star fortifications were further developed in the late fifteenth and early sixteenth century in response, primarily, to the French invasion of the Italian peninsula. The French army was equipped with new
cannons and
bombards that were able to easily destroy traditional fortifications built in the
Middle Ages. In order to counteract the power of the new weapons, defensive walls were made lower and thicker. They were built of many materials, usually earth and
brick, as brick doesn't shatter on impact from a cannonball like
stone does. Another important design modification was the
bastions that characterized the new fortresses. In order to improve the defense of the fortress, covering fire had to be provided, often from multiple angles. The result was the development of "star"-shaped fortresses.
They were employed by
Michelangelo in the defensive earthworks of
Florence, refined in the sixteenth century by
Baldassare Peruzzi and
Scamozzi.
The design spread out of Italy in the 1530s and 1540s. It was employed heavily throughout Europe for the following three centuries. Italian engineers were heavily in demand throughout Europe to help build the new fortifications.
The late-seventeenth-century architect
Menno van Coehoorn and
Vauban,
Louis XIV's military engineer, are considered to have taken the form to its logical extreme. "Fortresses... acquired
ravelins and
redoubts, bonnettes and
lunettes, tenailles and tenaillons, counterguards and crownworks and hornworks and curvettes and fausse brayes and
scarps and cordons and
banquettes and
counterscarps... that baroque profusion."
In the nineteenth century, the development of the exploding shell changed the nature of defensive fortifications.
The star-shaped fortification had a formative influence on the patterning of the Renaissance
ideal city: "The Renaissance was hypnotized by one city type which for a century and a half—from Filarete to Scamozzi—was impressed upon all utopian schemes: this is the star-shaped city."
Origins
The predecessors of star fortifications were
medieval fortresses, usually placed on high
hills. From there
arrows were shot at the enemies, and the higher the fortress was, the farther the arrows flew. The enemies' hope was to either ram the gate or climb over the wall with
ladders. Invading fortresses were quite understandably hard tasks for the invading force. Therefore, fortresses were in a key position in warfare.
When the newly effective maneuverable siege cannon came into military strategy in the fifteenth century, the response from
military engineers was to arrange for the walls to be embedded into ditches fronted by earth slopes so that they couldn't 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. As the walls became lower, they also became more vulnerable to assault.
Worse yet, the rounded shape that had previously been dominant for the design of turrets created "dead space" which was relatively sheltered from defending fire, because direct fire from other parts of the walls couldn't be shot around the curved wall. To prevent this what had previously been round or square turrets were extended into diamond-shaped points which would give storming infantry no shelter. The ditches and walls channeled attacking troops into carefully constructed killing grounds where defensive cannon could wreak havoc on troops attempting to storm the walls, with emplacements set so that the attacking troops had 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. Therefore, the shape was designed to make maximum use of
enfilade (or "flanking") fire against any attackers who should reach the base of any of the walls. The indentations in the base of each point on the star sheltered cannon located there. Those cannon would have a clear line of fire directly down the edge of the neighboring points, while their point of the star was protected by fire from the base of those points.
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 fort's 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
glacis, the open slope that lay outside the ditch, by creating defensive earthworks to deny the enemy access to the glacis 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 was caused by momentum from the impact of
solid shot. While only low explosives such as black powder were available, explosive shells were largely ineffective against such fortifications.
The development of
mortars,
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. Warfare was to become more mobile. It took, however, many years to abandon the old fortress-thinking.
Construction
It was also often necessary to widen and deepen the ditch outside the walls to create a more effective barrier to frontal assault and
mining. Engineers from the 1520s were also building massive, gently sloping banks of earth called
glacis in front of ditches so that the walls were almost totally hidden from horizontal artillery fire. The main benefit of the glacis was to deny enemy artillery the ability to fire point blank. The higher the angle of elevation, the lower the stopping power.
An example of the great expense of updating fortifications is the city of
Siena, which went bankrupt in 1544 attempting to update its city walls.
Notable Instances
trace italienne was at the
Papal port of
Civitavecchia, where the original walls were lowered and thickened because the stone tended to shatter under bombardment.
The first major battle which truly showed the effectiveness of
trace italienne was the defence of
Pisa in 1500 against a combined
Florentine and
French army. The original medieval fortifications beginning to crumble to French cannon fire, the Pisans constructed an earthen rampart behind the threatened sector. It was discovered that the sloping earthen
rampart could be defended against
escalade and was also much more resistant to cannon fire than the
curtain wall it had replaced.
The second siege was that of
Padua in 1509. A monk engineer named
Fra Giocondo, trusted with the defence of the
Venetian city, cut down the city's medieval wall and surrounded the city in a broad
ditch that could be swept by flanking fire from gunports set low in projections extending into the ditch. Finding that their cannon fire made little impression on these low ramparts, the French and allied besiegers made several bloody and fruitless assaults and then withdrew.
Effectiveness
According to
Geoffrey Parker in his article "The military revolution 1560–1660: a myth?", the appearance of the
trace italienne in early modern Europe, and the difficulty of taking such fortifications, resulted in a profound change in military strategy. "Wars became a series of protracted sieges", Parker suggests, and open-pitch battles became "irrelevant" in regions where the
trace italienne existed. Ultimately, Parker argues, "military geography", in other words the existence or absence of the
trace italienne in a given area, shaped military strategy in the early modern period. This is a profound alteration of the military revolution thesis originally proposed by Michael Roberts in his inaugural lecture delivered at the Queens University, Belfast, in 1955.
However, despite the advantages of these fortresses over earlier designs,
Machiavelli said: "Most first-class fortresses could be taken in roughly six to eight weeks." In his writing
The Art of War he states that "there is no wall, whatever its thickness that artillery won't destroy in only a few days".
Further Information
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