Trace italienne

A star fort, bastion fort or trace italienne, is a fortification in a style that evolved during the age of gunpowder when the cannon came to dominate the battlefield. It was first seen in the mid-15th century in Italy.

The design of the fort is normally a pentagon or hexagon with bastions at the corners of the walls. These outcroppings are present for the purpose of a total, panoramic view of the battlefield. Because of the bastions, archers and cannon operators can hit any target on the battlefield without having to lean over the wall and expose themselves. Many bastion forts also feature cavaliers, which are raised secondary structures based entirely inside the primary structure.

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 further the arrows flew. The enemies' hope was to either ram the gate or climb over the wall with ladders and overcome the defenders. For the invading force, these fortifications proved quite difficult to overcome, and accordingly, fortresses occupied a key position in warfare.

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 addition, an attacking force that could get close to the wall was able to conduct undermining operations in relative safety, as the defenders could not shoot at them from nearby walls. In contrast, the star fortress was a very flat structure composed of many triangular bastions, specifically designed to cover each other, and a ditch. In order to counteract the cannonballs, defensive walls were made lower and thicker. To counteract the fact that lower walls were easier to climb, the ditch was widened so that attacking infantry were still exposed to fire from a higher elevation, including enfilading fire from the bastions. The outer side of the ditch was usually provided with a glacis to deflect cannonballs aimed at the lower part of the main wall. Further structures, such as ravelins, tenailles, hornworks or crownworks, and even detached forts could be added to create complex outer works to further protect the main wall from artillery, and sometimes provide additional defensive positions. They were built of many materials, usually earth and brick, as brick does not shatter on impact from a cannonball as stone does.

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