Sally port, parapet wall and ditch visible at Fort Stedman , Petersburg National Battlefield, photoby Jon Buono.
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Military Earthworks Terms
Abattis or Abatis (Fr.) -- felled trees,
arranged in the form of a hedge with trunks aligned and anchored in a
shallow ditch. Branches were sharpened and interlaced pointing toward
the enemy. Its purpose was to prevent surprise and to delay an attacking
force within range of defensive weapons. Sometimes called a slashing.
Active Defense - strategy of defending a line by maneuver
Advanced Works -fortifications in advance of but still
within firing range of the main works.
Angle - where two faces of a fortification meet. See
Salient and Reentering Angles.
Apex - foremost salient angle of a fortification,
that which protrudes farthest toward the enemy.
Approach - a trench dug to get closer to the enemy line,
called a sap in siege operations.
Artillery Strong Point - a battery, redoubt,
or bastion that served to anchor a larger system of fortifications.
Artillery Works - earthworks designed to protect artillery
and to provide an effective field of fire.
Back-ditch or Interior Ditch - ditch
dug behind a parapet. See Ditch.
Banquette (Fr.) or Firing Step - a
shelf dug behind a parapet that allowed a defender to step up from the
ground to fire over the parapet, then step back down under cover to reload.
A banquette was only necessary when the parapet was higher than a man's
armpits. It was a common feature associated with prepared fortifications,
curtains, and detached works, such as redoubts. If a banquette
survives, it is often blurred by soil eroding from the parapet.
Balk - a narrow barrier of earth within the ditch of
an earthwork that was purposely left unexcavated. Balks sometimes marked
divisions between units in the line. A balk might also serve as the base
for a traverse made of logs.
Barbette (Fr.) - artillery positioned to fire over the
parapet rather than through an opening in it. See Embrasure.
A cannon firing en barbette had an unrestricted (180-degree) field
of fire, but its gunners were more exposed to fire than one firing en
embrasure. A barbette gun was raised to fire over the parapet by
means of a large carriage or by a gun platform built up to the appropriate
height. See Gun Platform.
Bastion (Fr.) - an angular work that projected outward
from the main faces of a fortification. Its purpose was to eliminate
defilade by directing fire along the front of an adjacent curtain
wall. Like a lunette, a bastion consisted of four parts: two faces
forming a salient angle oriented towards the enemy, and two reentering
flanks that directed fire sideways across the faces of adjacent
bastions. A curtain (or curtain wall) connected two or more bastions.
Bastion Line - a series of bastions joined by short
Bastioned Fort - an enclosed earthwork with bastions
in the angles to provide fire along the fronts of the connecting curtains.
Battery - an artillery unit or a fortification designed
to defend an artillery unit.
Berm or Berme (Fr.) - narrow ledge
or shelf left at grade to separate the scarp of the ditch and the
exterior slope of the parapet. When constructing high-relief defenses,
workers stood on the berm to relay earth from the ditch up onto the parapet.
The berm was sometimes left to retard slumping of the parapet, but many
engineers felt that it assisted attackers in scaling the parapet and had
it pared down after construction. Soil eroding from the parapet will
typically blur a berm's outline.
Blockhouse - building constructed of heavy logs in
the shape of a square, rectangle, or cross, to serve as a strong point
for infantry or artillery. A ditch was often excavated around the exterior
with the spoil thrown up against the wooden structure as a protection
against fire and gunfire. Often part of the first floor of a blockhouse
was below ground, while the upper floor, pierced with loopholes and embrasures,
was built with an overhang so that defenders could fire down around the
base of the structure. Blockhouses were used to defend railroad trestles,
bridges, and depots, or served as a "keep" or place of final refuge in
a larger fortress or stockade. The excavations associated with many blockhouses
survive, although timbers were often scavenged for other uses. Some had
brick or stone flooring and fireplaces.
Bombproof - a log or plank room or bunker covered over
with earth to protect troops from artillery fire. A surviving bombproof
appears as a large mound of earth, sometimes with an elongated depression
in the top where underlying timbers have collapsed or in the side where
the entrance used to be. See Magazine.
Bottom of the Ditch - flat space at the base of the
ditch that separated the scarp and counterscarp.
Boyau (Fr.) - a communication trench, a sap pushed
forward toward the enemy. Typically constructed in a zigzag pattern to
prevent exposure to direct fire from the front.
Breaching Battery - a battery constructed during siege
operations to enfilade a portion of the enemy's defenses or to batter
down the enemy's walls or parapets.
Breastwork - a linear earthwork that was tall enough
to cover the chest of a man standing behind it. A breastwork could also
be constructed of ad hoc materials, such as logs, stones, barrels, or
cotton bales. The term is used very generically.
Bulwark - See Rampart.
Capital - the imaginary line that bisects an earthwork's
Casemate - enclosed and roofed-over artillery position.
The gun fired through an opening called an embrasure. Casemates
vaulted with stone were a basic component of permanent masonry fortifications.
Casemates were constructed only rarely in the field with logs and earth.
Cavalier - See Keep.
Cheek - side of an embrasure, often reinforced
by gabions or sandbags.
Caponière (Fr.) - projection from the front of a curtain
wall that enabled infantry or artillery to fire into an exterior ditch.
Cheeks - sides of an embrasure, often reinforced
with gabions, sandbags, or logs.
Chevaux-de-frises (Fr.) - portable obstacles built of
logs with projecting sharpened stakes, joined together by chains; called
"horses of Friesland" where the device was invented in the mid-1600s.
Circumvallation - siege lines built to "invest," or
enclose, the enemy's defenses. See Countervallation.
Citadel - See Keep.
Column of Fire - a volume of fire directed perpendicular
to the parapet. Entrenched soldiers tended to fire directly to their
front when under attack, rather than side to side. To deliver fire where
it was most needed, engineers changed the orientation and relationships
of a fortification's faces and flanks. Each segment of
parapet had a specific column of fire that swept the front or interlocked
with fire from an adjacent segment.
Command - height of an earthwork above grade.
Communication Trench - a ditch and parapet that connected
one part of an entrenchment with another to move troops and supplies.
These were sometimes simple shelter trenches, serving as arteries to direct
reserves to some portion of the line. Called a covered way if
deep enough to conceal movement.
Continuous Line - a line of fortifications presenting
a solid front to the enemy. Parapets, or Curtains, connected all of the
artillery strong points on the line. See Lines at Intervals.
Corbeil or Corbeille (Fr.) - a form
of gabion; a small wicker hamper wider at the top, placed in a
row along the parapet and filled with earth. The tapered shape left a
musketry loop-hole between corbeils.
Corduroy Road - logs laid side-by-side in a roadbed
to make it passable in wet weather. The same technique was often applied
to gun platforms to support artillery pieces.
Counterbattery Fire - artillery fire directed at the
enemy's artillery in an attempt to silence or disable the guns. Because
of the threat of counterbattery fire, artillery positions were typically
built stronger and more massive than adjacent infantry entrenchments.
Countermining - See Mine.
Counterscarp - outer or exterior slope of a ditch.
Countervallation - siege lines built in conjunction
with lines of circumvallation to protect the rear of the besieging
force from assault by a relief force or from raids.
Covered or Covert Way - in permanent
fortifications, a walkway extending around the outside of the moat or
ditch of the main line; in fieldworks, a ditch and parapet designed to
protect and conceal the movement of troops and supplies to the front lines
from camps or supply caches in the rear. A covered way was not "covered,"
in the sense of being roofed over; it provided cover from gunfire.
Cremaillière (Fr.) or Indented Line -- a stepped or
saw-toothed line of fortifications, designed to generate crossing fires
all across the front of the line.
Crest - See Superior Slope.
Crossing or Interlocking Fire - fire
that converged on the same target from two different points. When laying
out a line of defense, engineers sought to generate interlocking fire
whenever possible. See Column of Fire.
Crownwork - a detached earthwork open at the gorge,
formed of a central bastion and two flanking demilunes with
two long flanks extending to the rear and inclining toward the
Cunette (Fr.) - a narrow drainage ditch
running along the bottom of a trench. Drainage was a continual concern
whenever an earthwork was occupied for any length of time. Drainage ditches
have been observed to survive, typically within semi-permanent forts,
siegeworks, and larger batteries.
Curtain or Curtain Wall - a straight
line of parapet that connected two bastions or artillery strong
points, technically with an exterior ditch.
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