Editing Glacis

{{Short description|Protective slope built into a fortification}}
{{Other uses}}
{{Use mdy dates|date=October 2018}}

[[File:Glacis.png|thumb|right|Diagram showing upward sloped glacis]]
A '''glacis''' ({{IPAc-en|ˈ|ɡ|l|eɪ|.|s|ɪ|s}}, {{IPA|fr|ɡlasi|lang}}) in [[military engineering]] is an artificial slope as part of a medieval castle or in [[bastion fort|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]]''.

A ''glacis plate'' is the [[sloped armour|sloped]] front-most section of the hull of a [[tank]] or other [[armoured fighting vehicle]].

==Ancient fortifications==
[[File:Tel_Esur_(6).JPG|thumb|Middle Bronze Age glacis in [['En Esur]], [[Israel]]]]

A glacis could also appear in ancient fortresses, such as the one the [[ancient Egypt]]ians built at [[Semna (Nubia)|Semna]] in [[Nubia]]. Here it was used by them to prevent enemy [[siege engine]]s from weakening [[defensive wall]]s.

[[Hillforts in Britain]] started to incorporate glacis around 350 BC. Those at [[Maiden Castle, Dorset|Maiden Castle]], Dorset were {{convert|25|m|ft}} high.{{sfn|Dyer|1992|p=19}}

==Medieval fortifications==
[[File:Krak des Chevaliers 14.jpg|thumb|[[Crac des Chevaliers|Krak des Chevaliers]], a medieval Crusader castle in Syria. The south face of the inner ward with its steep glacis.]]
Glacises, also called [[Talus (fortification)|taluses]], were incorporated into medieval fortifications to strengthen the walls against undermining, to hamper [[escalade]]s and so that missiles dropped from the battlements would ricochet off the glacis into attacking forces.{{sfn|Decaëns|Dubois|2010|p=17}}

Towards the end of the medieval period some castles were modified to make them defensible against cannons. Glacis consisting of earthen slopes faced with stones were placed in front of the curtain walls and bastions (towers) to absorb the impact of cannon shots or to deflect them. Towers were lowered to the same height as the curtain walls and converted into gun platforms.{{sfn|Stokstad|2005|p=84}}

==Early modern European fortifications==
{{main|Bastion fort}}
Early modern European fortresses were so constructed as to keep any potential assailant under the fire of the defenders until the last possible moment. On natural, level ground, troops attacking any high work have a degree of shelter from its fire when close up to it; the glacis consists of a slope with a low grade inclined towards the top of the wall. This gave defenders a direct line of sight into the assaulting force, allowing them to efficiently sweep the field with fire from the [[parapet]]. Additionally, but secondarily, the bank of earth would shield the walls from being hit directly by cannon fire.{{sfn|Jackson |1911}}<ref>{{cite web |url=http://fortadams.org/discover-the-fortress/the-terminology-of-a-fortress/ |title=The Terminology of a Fortress:Glacis |publisher=www.fortadams.org|access-date=14 June 2014}}</ref>

Though defenders on high ground already have a direct line of sight, a glacis allows the [[field of fire (weaponry)|field of fire]] to be swept more efficiently by minimizing changes to the angle of their guns while firing.  Furthermore, the glacis prevents attacking cannon from having a clear shot at the walls of a fortress, as usually these cannot be seen until the glacis is crossed and the ditch, bounded on either side by the smooth, masoned scarp and [[counterscarp]], is reached.{{sfn|Jackson |1911}}

==Armored vehicles==
[[File:Icon tank body.png|thumb|left|250px|The glacis of a [[tank]]'s armor is the sloped part at the front, marked in red.]]
The term ''glacis plate'' describes the sloped front-most section of the hull of a [[tank]] or other armored fighting vehicle,<ref>{{cite web |publisher=Encarta Online Dictionary |url=http://ca.encarta.msn.com/encnet/features/dictionary/DictionaryResults.aspx?refid=1861675459 |title=Glacis plate |date=14 December 2008 |archive-url=https://archive.today/20240524175858/https://www.webcitation.org/5kwq0aRcn?url=http://ca.encarta.msn.com/encnet/features/dictionary/DictionaryResults.aspx%3Frefid=1861675459 |archive-date=24 May 2024 |url-status=dead }}</ref> often composed of upper and lower halves.  In a head-on-head armored engagement, the glacis plate is the largest and most obvious target available to an enemy gunner.

[[Sloped armour]] has two advantages: many projectiles will deflect rather than penetrate; those that attempt to will have to travel on a longer diagonal route through any given thickness of armor than if it were perpendicular to their trajectory.

[[Anti-tank mine]]s that employ a [[tilt-rod fuze]] are also designed to detonate directly underneath the glacis plate. As a result, it is generally the thickest, most robust armored section of a tank, followed by the turret face and [[gun mantlet]].
{{-}}
==Gallery==
<gallery>
File:Maiden Castle, Dorchester..jpg|Iron Age ramparts and ditches in [[Maiden Castle, Dorset|Maiden Castle]].
File:Montlouis fort1.JPG|Glacis, [[Mont-Louis]] Fortress, [[Pyrénées-Orientales]], France
</gallery>
==See also==
* [[Fortification]]
* [[Siege]]

==References==
{{reflist}}
==Bibliography==
{{Wiktionary}}

*{{cite EB1911|wstitle=Fortification and Siegecraft|volume=10|pages=679–725|first=Louis|last=Jackson }}
*{{Cite book|title=Caen Castle: A Ten Centuries Old Fortress|publisher=Publications du Crahm|year=2010|isbn=9782902685752|editor-last=Decaëns|editor-first=Joseph|edition=illustrated|page=[https://books.google.com/books?id=qxqvtJg9FQsC&pg=PA17 17]|editor-last2=Dubois|editor-first2=Adrien}}
*{{Cite book|last=Dyer|first=James|title=Hillforts of England and Wales|publisher=Osprey Publishing|year=1992|isbn=9780747801801|edition=illustrated, revised|series=Shire Series|volume=16|page=[https://books.google.com/books?id=wqEBPHRcSzQC&pg=PA19 19]}}
*{{Cite book|last=Stokstad|first=Marilyn|title=Medieval Castles|publisher=Greenwood Publishing Group|year=2005|isbn=9780313325250|edition=illustrated, annotated|series=Greenwood guides to historic events of the medieval world|page=[https://books.google.com/books?id=_YjJc_c4BxsC&pg=PA84 84]}}

{{Fortifications}}

[[Category:Fortification (architectural elements)]]
[[Category:Vehicle armour]]