Line, Entrenched

Temporary fortifications designed to cover an extended position were referred to as entrenched lines. Entrenched lines could either be composed of a continuous line of nearly uninterrupted parapet or consist of any number detached works separated by more or less wide intervals. Entrenched lines might also combine both detached works capable of an independent defense with continuous stretches of parapet or trench connecting the detached works. Entrenched lines were also defined by their purpose as Entrenched Positions, Entrenched Camps, Lines of Circumvallation and Lines of Countervallation. An entrenched position can be roughly defined as any line of temporary works constructed for the purpose of protecting a position that either was presently occupied or might be assumed by an army acting on the defensive. This included lines constructed to cover important strategic points (such as the defenses of Washington, D.C.) and hastily constructed works intended to cover the front of an army in the immediate presence of the enemy. An entrenched camp was, as the name implies, a line of works constructed for the purpose of protecting an army's cantonment or camp against an unexpected enemy attack and assist an army in its winter quarters to maintain its position near the enemy (such as Fortress Rosecrans). By the middle period of the nineteenth century lines of circumvallation and countervallation had practically fallen out of use; a line of countervallation was constructed to enclose a besieged fortification and prevent the garrison from attempting to break out of the fortified place. A line of circumvallation was constructed to protect the rear of a besieging army from enemy field armies attempting to relieve the besieged garrison. The two together protected a besieging army's camps and depots of material.

Entrenched lines were also defined by the general outline of the works composing them and means provided by that outline of producing crossing columns of fire for their close defense. The most common types mentioned in period manuals include continuous lines such as redan lines, tenaille lines, cremaillere lines, bastion lines, and lines with intervals. Redan lines were basically simple lines of parapet or trench with projecting redans at intervals that were intended to produce columns of fire that crossed in front of the currents connecting the redans. Tenaille lines were composed of an alternating series of regularly spaced salient and re-entering angles. Cremaillere lines combined a connected series of faces broken forward from the general direction of the line that were joined by short flanks that produced columns of fire across the faces. Bastion lines were composed of a series of flat bastions (or lunettes) connected by curtains. Another type of line not dealt with in most manuals was the irregular indented line that was composed of flattened and irregular alternating salient and re-entering angles; these were similar in some regards to tenaille lines with the faces adapted in both length and angular orientation to take advantage of a fortified position's terrain. These types of continuous lines could only be applied to positions that could not be turned and were used when the defending army did not expected to deliver a counter blow to the enemy army assaulting the lines. Lines with intervals were generally composed of works capable of an independent defense with their faces oriented to project crossing columns of fire across the intervals between the works. Theory generally specified a main or retired line of enclosed works (redoubts) with an advanced line of works open at the gorge (redans or lunettes). This type of line was particularly useful for a defending army that was strong enough to assume a tactical offensive as soon as the army assuming the offensive had been disordered and thrown into confusion by its attack on the detached works.

A variety of different types of lines were adapted to fortify positions during the American Civil War. The defenses of Washington, D.C. (and other important cities) combined detached enclosed field works sited on commanding ground with nearly continuous lines of rifle trenches that connected the detached forts. The Williamsburg (Virginia) line across the Yorktown Peninsula and Pemberton's original line of defense across James Island, South Carolina (Defenses of Charleston) were both laid out as lines with intervals The first defensive line (Maury's Line) constructed to protected Mobile, Alabama was a fairly regular redan line that included several enclosed works and lunettes. Camp Parapet and the Company Canal defense line that covered the northern approaches to New Orleans were both typical cremaillere lines; the former's flanks were anchored on large irregular enclosed field works. Fort Pickering at Memphis, Tennessee had its outer line laid out as an irregular indented line.

January, 2003