Fort Terminology

[jrweaver]

The ditch of a fort is the area immediately outside the fort that has been excavated to a lower elevation than the country. It can be wet - water filled to something deeper than the head of a soldier - or dry. A wet ditch is often called a moat, reminiscent of a moat around a castle.
The purpose of a ditch is threefold: it serves as a barrier to an attacker; it increases the effective height of the scarp without exposing additional masonry; and provides earth for the ramparts and coverface. A dry ditch also creates a confined killing zone immediately outside the walls of the fort.
The wet ditch of Fort Monroe:

The wet ditch at Fort Pulaski, Georgia, on Cockspur Island:

The dry ditch at Fort Morgan. The trench in the middle of the dry ditch is called a cunnette, and provides drainage to keep the ditch dry.

The dry ditch at Fort Barrancas.

 

[jrweaver]

The counterscarp is the wall defining the outside of the ditch, opposite the scarp of the fort. The counterscarp provides a barrier to attack, as the attacker must scale down the wall to approach the fort. The counterscarp is tall enough that a jump into the ditch would be unrealistic for a soldier with weapons and accoutrements, therefore scaling ladders would be required.
The counterscarp also serves to assist in creating a killing zone in a dry ditch. Grapeshot and cannister shot fired down the ditch would ricochet of the scarp and counterscarp, creating a web of shot bouncing around the ditch.
The counterscarp of Fort Tompkins, defenses of New York City at The Narrows. Note that the brick chimney was a later addition, there would have been no obstructions to flanking fire along the ditch during the defensive period of the fort.

 

[jrweaver]

A structure that can be part of the outworks or part of the fort is the caponier (pronounced cap on YEAR). If a caponier is attached to the main fort, it is considered part of that work. If a caponier, however, is not attached to the main fort, it is considered an outwork.
A caponier can have either one or two functions. By definition, it must be designed to provide a defense of the ditch, therefore all caponiers have that function. A sub-class of caponier also provides a passageway. The Third System had caponiers that were part of the main fort as well as caponiers that were detached. It also had caponiers attached to the main fort that served as passageways as well.

A detached caponier located at Fort Hamilton, defending The Narrows between the inner and outer harbors of New York City.

The caponier at Fort McClary that is attached to the main fort:

The interior of the caponier at Fort McClary:

A caponier at Fort Tomkins that provided a passageway as well as a defense of the ditch: