REDAN is the simplest kind of work employed in field fortification, and it consists generally of a parapet of earth, divided on the plan into two faces, which make with one another a salient angle, or one whose vertex is towards the enemy. Existing alone, the work is capable of making but a feeble defence, since its faces are not defended by any flanking fire; and, being open at the gorge or rear, the enemy may easily enter it in that direction. It can therefore be bf use only at an outpost, to afford a momentary cover for troops who are to retire when a superior force advances against them. A redan may however be advantageously placed to cover the head of a bridge, the entrance into a village, or defend the ground in front of some strong rcdout ; a series of them may also be constructed along the front of an army, in order to strengthen the position and cover the artillery ; and, in all these situations, the defects above mentioned cease to exist, since in the first case the gorge is protected by the river, and in the others the faces and gorges are defended by the works or by the troops in the rear.
When it is required to defend any pass immediately on the right or left of redans, flanks, making salient angles with the faces at points now the extremities of the latter, are given to them, so that they then become what are also called bastions or lunettes ; and the necessity of having a crossing fire for the defence of the ground in front, when the redans are not flanked by other works, has at times induced engineers to break the lines of parapet near the gorges, so as to form re-entering bends, and thus constitute a wing on each side at a right angle with the face.
Among the works constructed, in 1810, for the defence of Lisbon, redans were frequently placed on projecting knolls, in front of the great redouts, in order to flank the ground which was unseen from the latter : their gorges were protected by palisades, or by parapets, sufficiently slender to have been demolished by the artillery of the principal work, had the enemy succeeded in capturing them ; and good communications, covered by the inequalities of the ground, or by earth purposely thrown up, were formed in order to allow the defenders, if necessary, to retire in security. The strong stone windmills, which in that country are often built on salient knolls of ground, were occasionally covered by redans of earth ; and thus were formed good defensive posts, to each of which the mill served as a reduit or keep. During the struggle in the south of France, in 1813, Marshal Soult caused redans to be constructed as outworks, one below another, on the descending tongues of land which project from the main chains of heights whose summits he had crowned by strong redouts.
Two redans connected together, so as to leave one re-entering angle in front, form a queue d'hyronde ; and the name of bonnet de pear() has been sometimes applied to a work consisting of three redans so placed.