Civil War Field Fortifications

Redan Lines

A standard redan line consisted of a series of equal sized redans spaced at regular intervals and connected by straight stretches of parapet and ditch. Two common methods for arranging the redans differed only in the distance allowed between the capitals of the redans' salient angles. D. H. Mahan described a standard redan line in his Complete Treatise on Field Fortifications that that placed the salient angles of collateral redans 180 yards apart to produce an angle of defense 160 yards long. Each redan had a 60 degree salient angle with faces 60 yards long. Egbert Viele resurrected Vauban's redan line, originally intended as a line of circumvallation, in his 1861 Handbook for Active Service. Though Viele incorrectly identified the length of the line of defense as the distance between salient angles, Vauban's line had the capitals of each redan 50 yards long from salient to base, 60 yards wide at the gorge, with collateral redans connected by curtains 200 yards long. The lines of defense between collateral redans was about 235 yards. Both methods produced redans in the form of equilateral triangles that were too far apart to provide flanking fire from the face of one redan across the salient angle of the next in the line.  Mahan's line required a greater number of redans with increasing the strength of the line. Neither allowed reciprocal defense between the redans and curtains while both left a very large area in front of the redan's salient angles that was neither covered by direct or flanking fire. Only the curtains were defended by a direct and flanking fire. While Mahan's line had a line of defense at the standard measure for close musket range, Vauban conceived his redans as battery positions and used close canister range as the standard for the length of the line of defense.

This problem was addressed by a third form. While all other properties of the line remained the same, the curtain joining two redans could be pushed forward at the central point to provide flanking fire across the redans' salient angles. This modification led to the introduction of tenaille lines, but the central salient of the curtain in a redan line was not as pronounced and was much more obtuse than the central small redan in tenaille line.

Both standard and modified redan lines were rarely used during the Civil War. Their simple regularity combined with their defects generally precluded their use. A section of Maury's Line composing the outer defensive perimeter for Mobile, Alabama was constructed in the form of a regular redan line and the line protecting Montgomery, Alabama was composed of small redans  (also called fleches) with faces 100 feet long spaced at regular intervals. When Wilson's cavalry captured Montgomery in 1865 the connecting curtains between the redans had not been completed.

If standard redan lines were uncommon, irregular redan lines were among the most common types of lines constructed during the Civil War. An irregular redan line was differentiated from a standard redan line by the irregular form of the redans and the varying distances between the redans. The determining condition for the shapes and intervals between redans was the terrain; irregular redan lines were designed individually to fortify specific positions without regard to the inherent defects imposed by the standard redan line forms. Perhaps the most famous and effective irregular redan line was constructed to protect Vicksburg, Mississippi. The sharp combination of ridges and ravines allowed the Confederates to place strong irregularly shaped redans at salient points along the length of their line and to support most of the redans with flanking fire simply by following the contours of ridges with irregular lines of rifle pits.

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