A glacis in military engineering is an artificial slope as part of a medieval castle or in early modern fortresses. They may be constructed of earth as a temporary structure or of stone in more permanent structure. More generally, a glacis is any slope, natural or artificial, which fulfils the above requirements. The etymology of this French word suggests a slope made dangerous with ice, hence the relationship with glacier.
Middle Bronze Age glacis in 'En Esur, Israel
Krak des Chevaliers, a medieval Crusader castle in Syria. The south face of the inner ward with its steep glacis.
Iron Age ramparts and ditches in Maiden Castle.
Glacis, Mont-Louis Fortress, Pyrénées-Orientales, France
A bastion fort or trace italienne 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.
Citadel of Jaca [es], Spain, an example of a bastion fort
Bourtange fortification, restored to its 1742 condition, Groningen, Netherlands
Plan of Tvrđa from 1861, in Osijek, Croatia
Model of the city of Naarden, Netherlands