A bastion fort or trace italienne (a phrase derived from non-standard French, literally meaning Italian outline) is a fortification in a style that evolved during the early modern period of gunpowder when the cannon came to dominate the battlefield. It was first seen in the mid-fifteenth century in Italy. Some types, especially when combined with ravelins and other outworks, resembled the related star fort of the same era. The design of the fort is normally a polygon with bastions at the corners of the walls. These outcroppings eliminated protected blind spots, called "dead zones", and allowed fire along the curtain from positions protected from direct fire. Many bastion forts also feature cavaliers, which are raised secondary structures based entirely inside the primary structure. Origins Their predecessors, medieval fortresses, were usually placed on high hills. From there, arrows were shot at the enemies. 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 when attackers directed cannon fire on to perpendicular masonry wall. In addition, attackers that could get close to the wall were able to conduct undermining operations in relative safety, as the defenders could not shoot at them from nearby walls, until the development of Machicolation. In contrast, the bastion fortress was a very flat structure composed of many triangular bastions, specifically designed to cover each other, and a ditch. 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. Bastion fortifications were further developed in the late