Vauban. having observed that the ravelin was sometimes abandoned by the defenders previously to assault, on account of the difficulty of retreating across the main ditch under a fire from batteries on the glacis before the bastions, constructed, in the interior of that work, another, which might afford the defenders protection till the coming night would permit them to retire in safety. This work was at first only a wall, pierced with los:Tholes for musketry and covering the steps at the gorge ; but when Vauban increased the size of the ravelin, he made this redout, or retrenchment, to consist of a rampart and parapet similar to those of the ravelin itself, as at Neuf Brisac ; and Cormontaingne subsequently enlarged the work, so as to render it a second ravelin, as at r [FORTIFICATION]. This spacious retrenchment contributes much to the prolongation of the defence of the ravelin, since it is capable of containing a large body of troops ; and each of its flanks carry three guns, whose fire might be directed against the counter-battery at the salient of the bastion, or might serve for the defence of the breach in the face of the latter, should the enemy attempt to make an assault before lie has obtained possession of the reduit. But to take this last, it would be necessary to breach its faces either by artillery or by mining ; and the passage of its ditches would be difficult under a close fire from the ramparts near the shoulders of the neighbouring bastlone.
In order that the defenders might be able to retain possession of the extremities of the myelin, near the main ditch, after the salient part may have been taken, retrenchments or coupures, as they are called, similar to the traverses, 1,1, &e., are recommended to be formed across the terreplein of the myelin. Behind these some of the defenders may retire, and keep up a firragaireit the enemy's lodgment near 7.,
When Vauban had ;enlarged the re-entering places of arms, I. (BASTION; FORTIFICATION], he retrenched the interior with stockades, t teeming the steps leading from the dos hoe in their rear, rovete the retreat of the defenders of the covered way; and Coe . about the same UAW, to Liar eatistructod trick wall., loopholes, in the places of arms, at Itergenop-Zootn, for the same purpose. But Cormootaingne, in order to render the &Imam of the places of alma snore obstinate, and to secure more effectually the retreat of the deteader, of the coremeloray, constructed the resorts, as w I with parapets of earth 12 or 11 feet thick ; anti be reveled the sides of their ditches, in order to dieniniala the risk of a surprise: he also rave them flanks, which he made perpendicular to the corered.way. that a fire of light artillery or musketry might be directed from there spinet the enemy %bile attempting to crown the salient, of the rarelin. These redonts more. orm corm the shoulders of the bastions and the portions of the curtain eiloeh aught be men and breached by a fire directed between the flake of the bastions and the tenailke ; and their fame are directed so that they cannot be enfiladed. The crest of their parapet is about four feet higher than that of the glecia in their front.
The adrenced works about a fortress are recommended to be retrenchesl with round towers of masonry, provided with upper and lower tiers of loopholes foe musketry. Thees are called safety redoubts ; and in klomtalembtvt's ' Fortification Porpendiculaire; such towers are con• strutted to carry artillery within the rampart of the enceinte.
For retry-alchemists in field fortification, see litoceimesr.