Glacis

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A glacis (/ˈgleɪ.sɪs/ or /ˈglæ.si/) in military engineering is an artificial slope of earth in the front of works such as fortifications, so constructed as to keep any potential assailant under the fire of the defenders to the last possible moment. On the natural ground level, troops attacking any high work have a degree of shelter from its fire when close up to it; engineers therefore raise such ground to form a glacis, which defenders can sweep with fire from the parapet. The glacis was originally designed to protect stone fortifications, as vertical walls could easily be smashed down by artillery fire. The glacis deflected incoming cannonballs by providing a springy, sloping surface which the cannonballs bounced off, landing behind the fragile stone fortifications.

More generally, the term glacis can denote 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.

1 Armored Vehicles
2 Geology
3 See also
4 References

[edit] Armored Vehicles

The term glacis plate describes the sloped front-most section of the hull of a tank or other armored fighting vehicle.^[1] In a head-on-head armored engagement, the glacis plate is the largest and most obvious target available to an enemy gunner. Anti-tank mines which employ a tilt-rod mechanism are also designed to detonate directly underneath the glacis plate. Resultantly, the glacis plate is generally the most thickly armored section of a tank, followed by the turret face and mantlet.

US M1A1 Abrams main battle tank, edited to identify features (glacis plate highlighted in green)

[edit] Geology

An erosional or depositional pediment, with little slope. Erosional glacis occur mostly in arid regions, and result from intense meteorization (weathering) and surface transport via laminar, episodic water flow.