FORTIFICATION. 159 



space is empty, and behind the parapet is an elevated terreplein. Then the 

 revetment wall {Jig> 33), which rises from the bottom of the ditch to the 

 bottom of the parapet, and is terminated above by a projecting coping, has 

 buttresses on the inner side {fig. 21, horizontal section through the revet- 

 ment wall, abc defg), and in rear of the same runs a subterranean gallery 

 for mines, the magistral gallery, which gives access to the system of defen- 

 sive mines, of which we shall say more hereafter. If the interior space of 

 the bastion is filled with earth, it is called a solid or full bastion ; it has then 

 usually an additional raised work, the cavalier, and is provided with bomb- 

 proof vaults (casemates). Fig. J9 gives the horizontal section of such a 

 bastion, ab c defg, having casemates in its interior space, of which fig. 20 

 shows the vertical section along the line ec (fig. 19, seen from the gorge). 

 The exit from the front of attack is always established in the centre of the 

 curtain and is subterranean, being carried by a vaulted passage under the 

 parapet. Fig. 22 shows such a passage (sally-port, postern) : aa is the 

 revetment wall of the main rampart ; b are the side walls, and c, the but- 

 tresses for strengthening the wall ; d, a separate vault for muster-place. 

 Fig. 23 shows the longitudinal, and fig. 24, the cross-section of such a 

 postern. Underneath this, usually, a drain is carried to lead off water. 

 Fig. 34 is a longitudinal section through the front of attack (fig. 1) : A is 

 the terreplein ; C, the curtain with the attached bastion ; E, the tenaille ; 

 F, the main ditch ; G, the terreplein of the ravelin, whose parapet is H ; 

 J is the ditch of the ravelin, and N, the covered way with the glacis. 

 R are the scarp and counterscarp revetment-walls ; I and G, their slopes. 

 The inscribed numbers are the measurements in feet. 



8. The system of Vauban has been still improved upon by the French engi- 

 neer Cormontaigne ; his system remained for a long while, down to the time of 

 Carnot and Montalembert, the favorite one, and many places were fortified by 

 it. The enceinte, ae g hfb (pi. 48, fig. 4), Cormontaigne draws, for the bas- 

 tions, A A, and the curtain, B, in the same manner as Vauban, with the differ- 

 ence only that the flanks are perpendicular upon the lines of defence. To 

 construct the ravelin, lay off, from the point where the counterscarps of the 

 main ditches intersect (fig. 1 g), 360 feet on the perpendicular bisecting 

 the curtain to C, and there is the salient of the ravelin, whose faces are 

 aligned upon the points k and i, which are advanced 90 feet from the 

 shoulder-points. In the ditches of the ravelin are placed the traverses, K. 

 The redoubt, c, of the ravelin runs parallel with the main work 36 feet from 

 it and receives flanks, D, which command the somewhat lower part, L, of 

 the main work. E is a covered way, from the tenaille, F, to the redoubt 

 of the ravelin. The salient places-of-arms of the covered way are defended 

 by traverses, and in the re-entering, H, the redoubts, I, are established. 

 The glacis, M, is shorter than in Vauban's svstem. 



9. The system of Count Cohorn, a renowned engineer living in Holland 

 at the time of Vauban, is of great value, especially for countries abounding 

 in water. One of his fronts is represented in fig. 10. It is constructed on 

 the interior polygon, its sides, A A, containing, for the hexagon, 900 feet. 

 The demi-gorges. A/ and Kk, are \ the polygon side, and the capitals, AD 



635 



