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a gently sloping embankment in front of the outside ditch of a fortress, long-term structure, or field fortification. The glacis was built for the purpose of improving the field of fire over terrain lying in front of it and for camouflaging and defending the fortification.
In Russian fortresses the main rampart sometimes had a glacis-like profile, so that frontal fire could be directed at the bottom of the outside ditch. In current long-term fortifications the glacis is not used, and in field fortifications (foxholes and trenches) a breastwork is set up. In architecture the glacis is the unbuilt space in front of a fortress (in front of the earth embankment or in its place if it has been destroyed). During a city’s development around a fortress, the glacis usually was turned into a garden or a square (for example, the Admiralty and Senate [now Decembrists] squares in Leningrad on the site of the 18th-century ditches and glacis of the Admiralty shipyard-fortress).