Bastion fort

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A bastion fort or trace italienne (a phrase derived from non-standard French, meaning 'Italian outline') is a fortification in a style developed during the early modern period in response to the ascendancy of gunpowder weapons such as cannon, which rendered earlier medieval approaches to fortification obsolete. It appeared 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 wall from positions protected from direct fire. Many bastion forts also feature cavaliers, which are raised secondary structures based entirely inside the primary structure.