Glossary of Fortification Terms as used in the American Third System of Masonry Coastal Forts, 1816-1867


Dec 9, 2020
Excerpted from A Legacy in Brick and Stone: American Coastal Defense Forts of the Third System, 1816-1867, by John R. Weaver II, Second Edition, copyright 2018, posted on this page with permission. All rights reserved.

Please note that terminology changes over time. This glossary is based on the terminology taught at the U.S. Military Academy at West Point and used by American engineers in the early-to-mid 19th Century. This primarily applies to "permanent" fortifications - those built from brick and stone - but most of the terminology can be applied to field fortifications as well. Also note that the engineers designing the forts used the terminology loosely - two different engineers might call a particular structure by different names. JRW

Abatis (ab ah TEE): An obstacle made from tree branches and brush that have been sharpened on the side facing the attacker.

Advanced: Toward the enemy or toward the expected direction of attack. In advance.

Advanced Work: A work in advance of a fort, generally within range of the cannon of the day.

Angle of Traverse: The angle through which a gun can be rotated. The pintel location, the embrasure size, and the carriage design determine this angle.

Approaches: Trenches dug by an attacker, generally parallel to or at a slight angle to the curtains of a fort. Also referred to as parallels. Approaches are used in the siege of a fort.

Banquette (bahn KET): The raised earthen or paved platform behind the parapet on which riflemen can stand when firing.

Banquette Slope: The earthen or paved slope leading from the banquet to the covered way or terraplein. Riflemen could use this slope for reloading their weapon while shielded from direct fire by the parapet.

Barbette (bar BET): The platforms behind the parapet on which guns are mounted, such that they can fire over the wall. Guns are said to be mounted en barbette when they are mounted on these platforms.

Barbette Tier: The top tier of a fort where guns are mounted en barbette rather than en casemate.

Bastion (BAST yun): A projection from the trace of the fort, usually at a salient, which allows flanking fire along the wall. A full bastion has two faces and two flanks; a demibastion has one face and one flank.

Battery: 1. A structure, generally smaller than a fort and usually open-backed, designed to mount guns. A battery is generally constructed at a location that does not require a fort.

Battery: 2. A group of gun emplacements, either within a fort or in the outworks of a fort. 3. A group of guns commanded by a single officer.

Blockhouse: A structure of heavy timber, masonry, or a combination of both. A blockhouse may be a stand-alone structure to guard a particular location, it may be used at a salient or along the curtain of a fort in lieu of a bastion, or it may be a central structure surrounded by an earthwork. A blockhouse often was a multistory structure with the second level having a larger trace than the first. The overlap would contain machicolations – openings to fire down on an attacker.

Bombproof: A structure protected from indirect or plunging fire; a place of refuge during a siege.

Breach: An opening created in a wall, most often during a siege. A breach is generally created by cannon fire or a mine.

Breast-Height Wall:
A revetment, generally masonry or wood, that protects defenders while allowing them to fire over the parapet. It may be used in outworks or the main work.

Breastwork: A breast-height wall that provides a defensive position.

Buttress: A projection from a wall to add strength and/or stabilize the wall. A buttress is generally triangular in shape.

Canister Shot: Containers filled with iron balls, usually ranging in size from three-fourths inch to two inches in diameter. On firing, the canister splits open discharging the shot in a shotgun-like pattern.

Caponier (cap un YAIR): A small, vaulted outwork designed to provide flanking fire along a wall, generally located in the ditch. A caponier may or may not be attached to the scarp wall. Also, a defensive passageway, generally located in a ditch or closing a ditch. Caponiers had loopholes, howitzer embrasures, or both on at least one wall.

Carnot Wall (CAR noh wall): A detached scarp; a scarp wall which is separated from the ramparts of a fort, usually by a chemin de ronde. A Carnot wall was an infantry-defense device that was considered expendable in a siege.

Carronade: A short-barrel cannon used for flanking fire, similar to a flank howitzer. Carronades were originally designed for shipboard use, but were also used for antipersonnel missions in forts.

Casemate (CASE mate): A vaulted, bombproof room of masonry construction, sometimes called a gunroom. It provides overhead protection to gunners, and allows tiers of guns to be stacked. Casemates may also provide firing positions for small arms, and may be used for quarters, kitchens, storage, and other sundry functions.

Castle: A tall fort. The term generally refers to a fort with multiple tiers of guns.

Cavalier: A work within a fort that is higher – generally 10-12 feet – than the mass of the ramparts. In the Third System, a cavalier was used to close the throat of the bastions of Fort Jackson.

Center-Pintle Carriage: A gun carriage with the pintle mounted at or near the center of the carriage, allowing a 360° rotation of the gun.

Chemin de Ronde (SHEH min deh RON dah): A pathway around the interior of the scarp wall of a detached-scarp fort, serving as a firing platform for riflemen.

Cheval-de-Frise: An obstruction consisting of pointed poles extending radially through a central axel. These were often used to block a breach in a wall, or as a barrier to a cavalry charge.

Citadel (SIT ah dell): A stronghold inside the scarp of a fort which serves as a defensive barracks and a last line of defense.

Command: To overlook a work or a plain. A work or location is said to command another work or location if it stands above it.

Cordon: A projection, often of rounded stone, at the junction of the scarp and the exterior slope. Its primary function was to protect the masonry from weather.

Counterfort: A buttress on the earthen side of a wall, generally either the scarp or the parade wall, to increase its strength. A counterfort is generally hidden by earth.

Countermine: A tunnel going outward from the fort, used as a defense against mining the fort walls. A countermine generally had areas in which explosives could be placed to cave in the mine of a siege force or to bring down a bastion of the fort if the bastion falls to an attacker (see also, Listening Galleries).

Counterscarp: The wall across the ditch from the scarp. The counterscarp served as a revetment as well as an obstruction to entry of the ditch by making it a significant drop to the level of the ditch.

Counterscarp Gallery: Casemated areas behind the counterscarp wall, allowing a cross-fire into the ditch. Counterscarp galleries generally contained howitzers at the corners, with loopholes in the remaining walls. Access is from the ditch or a tunnel under the ditch.

Coup de Main (KOO dah MIN): An assault of a fortification by storm, rather than by siege. A coup de main would allow the possession of a fort in a very short time period compared to that required by a siege.

Coverface: An earthen, earth-and-masonry, or masonry outwork designed to protect the scarp of the fort from siege guns. The earthen coverface at Fort Warren would provide protection of the scarp from cannon on nearby islands and mounted cannon en barbette. The “casemated coverface” at Fort Monroe was an all-masonry casemated water battery that increased the firepower of the fort.

Covert (KUV ert) Way, or Covered Way: The area above the counterscarp, covered by the guns of the fort but protected from view by an attacker by the parapet.

Crenel: An open-topped embrasure at the top of a wall. A crenel is defined by two adjacent merlons.

Crochets (croe SHAYS): Angled or curved paths around a traverse that spans a covert way, generally wide enough for only one soldier abreast to pass.

Crownwork: A very elaborate outwork consisting of two demibastions joined by curtains to a central bastion. Fort Adams has the only crownwork in the Third System.

Cunette: An open-topped drain, often in the center of a dry ditch. A cunette was used to keep a dry ditch free from water.

Curtain: The portion of the scarp between bastions.

Curtain Angle: The angle formed by the curtain and the flank of a bastion. Also called the flank angle.

Defensive Barracks: A stronghold inside the scarp of a fort which serves as a barracks and a last line of defense. Also called a citadel.

Demibastion (DEM mee BAST yun): A half-bastion; a bastion with only one face and one flank.

Demilune: Literally, "half moon." A demilune is a semicircular outwork, generally used for land defense. The term is used interchangeably with ravelin, but generally ravelin implies a salient while a demilune implies a semicircular face.

Detached Bastion: A bastion separated from the scarp wall, often by a ditch or chemin-de-ronde. The detached bastions in the Third System were connected to the main work by a gallery. This design, though differently implemented, was used for forts Scammel, Clinch, and Gaines.

Detached Scarp: A masonry scarp in advance of an earthen rampart, usually separated by a chemin-de-ronde. This allowed the destruction of the scarp wall during a siege without damaging the mass of the fort. Also called a Carnot Wall.

Detached Work: An independent work beyond the outworks of a fort, generally located outside of cannon range from the main work. The “Martello Towers” at Key West would be detached works to Fort Taylor.

Ditch: A low area, either wet or dry, which inhibits the passage of the enemy to the scarp wall. The ditch is located between the scarp and counterscarp wall. A wet ditch is usually referred to as a moat.

Drawbridge: A bridge, generally over the ditch, that controls entrance to the work and can be raised or pivoted to deny access.

Embrasure (em BRAY Shure): An opening in the scarp, the counterscarp wall, or the parapet which allows a cannon to fire through it. An open-topped embrasure, rare in the Third System, is also called a crenel.

En Barbette: The practice of mounting cannon on a platform (barbette) such that they fire over a wall rather than through an opening (embrasure) in that wall.

En Casemate: The practice of mounting cannon in a casemate such that they can fire through an embrasure.

Enceinte (awn SAHNT): The body or mass of a fort, inside the ditch.

Enfilade (en fill ODD) or Enfilading Fire: Fire from the side. Flanking fire

Escalade: An attack made by climbing over the parapet of a fort, usually using ladders.

Exterior Slope: The slope between the cordon and the superior slope. The exterior slope is usually the steepest slope on the exterior of the parapet. It is usually earthen, designed to absorb artillery fire.

Face: The side or sides of the fort which open onto the water, where the primary coastal guns will be located. On a bastion, the face is the wall of the bastion which is nearly parallel to the curtain.

Flank, or Cheek: The side. On a bastion, the flank is the portion which is most nearly perpendicular to the curtain of the fort. The flank of a bastion provided the primary fire along the curtain.

Flank Angle: The angle formed by the curtain and flank of a bastion or demibastion. Also called the curtain angle.

Flank Howitzer: A howitzer designed to fire the length of the ditch, usually from the flank of a bastion. A flank howitzer generally fired canister shot or grapeshot.

Flanking fire: Fire from the side. Enfilading fire.

Fortress: A fortification with a civilian population; a fortified city.

Fraises: A row of sharpened logs placed horizontally or angled downward. These were generally imbedded in an earthen rampart of a fort to inhibit escalade.

Front: The side of a fort. On an unbastioned fort, the front is measured from comer to corner. On a bastioned fort, it is measured from the salient of a bastion to the salient of the opposing bastion, including the curtain wall between the bastions.

Front Pintle or Fore Pintle Carriage: A carriage where the pintle is attached at or near the front, giving a limited arc of traverse. When firing through an embrasure, the pintle is at the throat of the embrasure and attaches to the carriage with a tongue – a flat piece of metal that passes through an opening below the embrasure. When mounted en barbette, the pintle is at the front of the carriage.

Gabion (GAB ee on): A bundle or open-topped cylinder filled with materials – often branches or stones – used to form a barrier. Gabions were used in temporary (such as siege) works and to fill breaches in a permanent fortification.

Gallery: A passageway, generally masonry or masonry revetted. A gallery differed from a caponier in that a gallery has no defensive mission and therefore has neither loopholes nor embrasures.

Glacis (glah SEE ): The gentle slope beyond the outworks, cleared of all obstructions, which an attacker must traverse to reach the fort.

Section View of a hypothetical Third System fort, showing diagrammatically the terms used in fortification design during this period. It should be noted that not all engineers followed the conventional terminology of the day, therefore some drawings are labeled with questionable names for fort components.

Plan view of a hypothetical Third System fort. Please note that this drawing and the previous drawing do not represent any particular fort, they are a representation to show typical components of a fort to demonstrate the nomenclature used during this period.

Gorge: The side or sides of the fort away from the water, where land defense is the primary concern. On a bastion, the gorge is the narrow portion of the bastion toward the parade, also called the throat of the bastion.

Grillage: A web of timbers, often placed in perpendicular layers, used as the foundation of a fort. Cedar was the most popular wood to use to form a grillage.

Guard Room: A room usually within the fort – exceptions are at Fort Warren and Fort Adams where the guard rooms are exterior to the fort – that guards the main sally port. A guard room generally has loopholes into the sally port, and often contains a cell for prisoners.

Hornwork: An elaborate outwork, consisting of two demibastions connected by a curtain. The only hornwork in the Third System is at Fort Schuyler.

Hot-Shot Furnace or Shot Furnace: A furnace for heating shot. A masonry structure, it consisted of a fire chamber below rails on which the shot would travel. A loading mechanism sat at one end and an unloading mechanism at the other. Hot shot was used to set fire to wooden ships, sails, and rigging. In several cases hot shot was used against a town to set it afire.

Howitzer: A short-barreled cannon. Flank howitzers generally were used for antipersonnel missions, firing canister shot. Seacoast howitzers (or siege howitzers) generally utilized a high angle of fire (between a gun and a mortar).

In Advance: Toward an attacker, or toward the likely route of an attacker.

In Battery: A gun in firing position, i.e., at the front of the lower carriage with its muzzle at the throat of the embrasure.

Interior Crest: The highest point of the parapet. The top of the superior slope.

Interior Slope: The vertical or near-vertical slope from the crest of the parapet to the banquette, or the terraplein if there is no banquette. This slope is generally masonry or wood.

Investment: The surrounding of a work in preparation for a siege, preventing resupply or reinforcement of the work. The time period of a siege is generally counted as beginning when the work is invested.

Land Front: The front of a fort facing the land, where a siege would take place. In the Third System, the land front was generally designed in the style of Vauban with protection of the masonry and levels of defense.

Listening Gallery: A tunnel extending beyond the scarp of a fort that is used to detect the sounds of the mining operations of a siege force.

Loophole: A narrow opening in a wall which allows a rifle or musket to fire through it. Also called a rifle slit.

Machicoulis Gallery: A protruding gallery that allowed firing through the floor, thus protecting the area along the scarp without the use of a bastion or caponier. The overhang of blockhouses often served as machicoulis galleries.

Magazine: The place for storage of powder inside a fort. The main (or storage) magazine would store the bulk of the powder, and day-use (or service) magazines would be secondary storage depots. Magazines were carefully designed to prevent sparks and to provide a dry atmosphere for the powder.

Martello Tower: A round tower of three or more floors mounting heavy artillery en barbette on the top level (generally one to three cannon) and infantry-defense weapons (howitzers, carronades, and small arms) on the lower levels. Based on a design in Corsica which successfully defended a harbor, the entrance was always on the second floor. This nomenclature was extended to encompass any tower-like small fort, whether round or rectangular and with or without outworks.

Merlon: A rectangular projection from the top of a wall. Crenels and merlons alternate on a crenellated wall.

Militia Artillery: A group of reserve soldiers who were trained in artillery drill. Militia artillery were used to supplement the regular garrison in Third System forts.

Mine: An underground excavation passing under a work. A mine could be filled with explosives that would be detonated to cause a breach in the defenses.

Moat: Another name for the ditch, usually implying a wet ditch.

Outworks: Works located within or beyond the ditch, i.e., works outside the enceinte of the fort.

Palisade: A wooden wall of sharpened stakes. On an earthwork fort, the palisade was generally located at the center of the ditch, shielded from artillery by the counterscarp.

Pan Coupe: A feature of an unbastioned fort, consisting of a wall that connects two curtains. It follows the trace of the gorge of a bastion in a bastioned fort, replacing a sharp salient with two broader salients.

Parade: The open area in the center of a fort, usually used for drilling troops, for barracks area, etc.

Parados: An earthen traverse located on the parade of a fort, parallel to the scarp. A parados prevented reverse fire on the ramparts and contained shot and shell passing over the ramparts.

Parallel: Trenches dug by an attacker, generally parallel to or at a slight angle to the curtains of a fort. Also referred to as approaches. Parallels are used in the siege of a fort.

Parapet: The low wall along the top of the rampart, generally masonry or masonry-revetted earth, which protects the artillery and the banquette. The highest point of the rampart.

Pintle: The pin around which a gun carriage rotates. A front-pintle carriage for a gun mounted en casemate generally has the pintle at the narrowest part (throat) of the embrasure. A center-pintle carriage, sometimes used on a barbette emplacement, allows a full 360-degree traverse of the gun.

Place d'Armes (PLAHSS deh ARMS): A gathering place for counterattacking forces. A place d'armes can be within a fort or a part of the outworks of a fort. Within a fort, a place d’armes is an earthen embankment that replaces casemates, mounting guns en barbette. In outworks, a salient place d’armes is located beyond the salient of a bastion or pan coupe; a reentering place d’armes is located at the midpoint between bastions or pans coupe at a reentering (obtuse) angle.

Polygonal Fort: A fort with the trace of a polygon, as opposed to a bastioned fort or a fort with a rounded trace. In the later Third System, a five-sided truncated hexagon with demibastions at the gorge was often used for a polygonal fort.

Portcullis (por cue LEE ): A wooden or iron gate which bars access but not sight, often on the inner side of a sally port. This allows the attacker to be trapped within the sally port while under fire from the defenders. A portcullis generally opened vertically.

Postern (POST ern): The "back door" of a fort. Posterns are secondary entrances leading through the ramparts and either into or over the ditch. A postern often connect to a ravelin, an exterior batteries, or another outwork.

Rampart (RAM part): The full thickness of the walls of a fort, including the casemates.

Ravelin (RAVeh lin): A V-shaped outwork, usually with an open back. Ravelins were placed in advance of either a curtain or the gorge of a fort, giving protection to the scarp and/or providing additional batteries.

Redan (reh DAHN): A small, V-shaped, open back outwork placed in advance of either a curtain or the gorge of a fort, protecting the scarp and providing additional batteries.

Redoubt (reh DOOT): Technically, an unbastioned fort some distance from the main fort which is designed to form the first line of defense and provide early warning of an attack. In the Third System, redoubts sometimes had demibastions and the distance to the main fort varied greatly. At Fort Adams, the guard house exterior to the fort was also called a redoubt.

Reentering: An angle pointing toward the fort; an angle of greater than 90 degrees, such as where a bastion meets a curtain.

Revet: To face an embankment, usually with masonry or wood, to sustain it.

Revetment: A depressed area sustained by masonry or wood, with the surrounding earth providing protection.

Salient: An angle pointing away from the fort; an angle of less than 90 degrees, the "point."

Sally Port: The main entrance or entrances to a fort, often including layers of defense against an invader. The sally port is generally located in the gorge wall.

Scarp, or Scarp Wall: The perimeter wall of the fort.

Seacoast Front: The front of a fort facing the water, designed to control passage and/or dominate a harbor. In the Third System, the seacoast front was generally designed in the style of Montalembert with unprotected masonry providing multiple tiers of guns.

Shell: A projectile fired from a cannon or mortar that has a hollow interior, that is filled with explosives.

Ship-of-the-line, or capital ship: A large warship. A ship-of-the-line was generally a three-masted sailing ship with three of four decks of cannon. These large ships were the principal warships of a fleet prior to the use of ironclads.

Shot: A solid iron projectile fired from a cannon. Shot had far more momentum than shell, but did its damage through momentum only.

Shoulder: The place on a bastion or demibastions where the face and the flank meet. The shoulder of a bastion is generally at its widest point.

Shoulder Angle: The angle formed by the face and flank of a bastion or demibastion.

Siege: The protracted taking of a fort, beginning with investment and continuing through the breaching and ultimate reduction of the work. By the time of the Third System, it was understood that ultimately no fort could hold out indefinitely to a siege.

Sole: The bottom of an embrasure or loophole.

Star Fort: A fort with a tenaille trace, i.e. a fort whose ramparts are multiple salients emanating from the parade. There were no star forts in the Third System. Second System Fort Wood, now the base for the Statue of Liberty, is a star fort.

Superior Slope: The slope that reaches the crest of the parapet. The superior slope is usually the shallowest slope of a parapet.

Tenailles (ten EYE): Low, detached outworks, generally placed in the ditch, usually between bastions. Tenailles usually have casemated demibastions at the ends with an earthen mass between the casemates. This mass is sometimes revetted with masonry.

Terraplein (TARE a pleh): The area atop the ramparts behind the banquette and parapet, supporting the barbettes.

Throat: The narrowest part. On a bastion, the narrow portion between the flanks, nearest the parade. On an embrasure, the narrowest portion of the opening.

Totten embrasure: An embrasure reinforced with iron, developed by J. G. Totten. These embrasures provided a smaller opening and a wider angle of traverse of the cannons than European embrasures. Totten embrasures usually, but not always, utilized Totten Shutters.

Totten shutters: Iron doors which close an embrasure between cannon firings. This intricate system was developed by J. G. Totten.

Tower Bastion: A bastion of reduced size, often of significant height.

Trace: The line defining the exterior of the enceinte, or body, of a fort. The trace is generally referred to by the geometric figure that defines it.

Traverse (trah VERSE): 1. An earthen or masonry-revetted earthen mound which breaks the open area of the terraplein, separating men and guns to eliminate enfilading fire and minimizing damage from exploding shells. Traverses also allow defense of portions of the ramparts when other portions have been stormed, and often house bombproofs and magazines. 2. The arc of stone on which the rear wheels of guns travel. The individual stones are generally referred to as traverse blocks. The iron rail that the wheels travel on is generally referred to as a traverse rail.

Water Battery: A water battery is a group of cannon facing seaward and firing as a unit. A battery was generally commanded by a single officer. Use of the term water battery often implies a separate, detached work housing a group of cannon.

Work: A fortification. This is the broad term that applies to forts, fortresses, towers, redoubts, batteries, etc.


Dec 9, 2020
Here are three pictorial views of the parts of a fortification, as a supplement to the glossary. Like the glossary, they are excerpted from A Legacy in Brick and Stone, Copyright 2018, all rights reserved. Enjoy!
Glossary Plan Layout color smaller.jpg

Glossary Section Diagram Color.jpg

Glossary Parapet Detail.jpg