FORTIFICATION. 157 



3. The Chevalier De Ville, who lived under Louis XIII., improved the 

 earlier methods, and fixed all bastion angles at 90°. De Ville constructed 

 his system upon the interior polygon, and made the length of the flank 

 equal to the half gorge of the bastion (fig. 5). For this he divided the 

 polygon side into six equal parts, one part on each extremity being the 

 demi-gorge of the bastion, AA, and the other four parts the curtain, C. 

 By erecting perpendiculars at the two first points of division, he obtained 

 the position of his flanks, BB, which he made equal to the demi-gorge, and 

 thus determined the shoulder points, k and c. From these he laid off" upon 

 the prolonged capitals, angles of 45°, and thus obtained the points a and 6, 

 through which and the shoulder points he drew the lines of the faces, which 

 intersect at m. To construct the orillon, he divided the flank into three 

 equal parts, and drew, through the second points of division, i and d, and 

 the points a and h, the lines ah and he, which intersect at /. Setting oflf 

 now, from d and i towards e and h, f of the flank, and drawing, parallel to 

 the flanks, the lines ef and gh, the orillon was completed. De Ville, however, 

 did not do away with the front part of the flank, but only established it some- 

 what deeper than the drawn back flank, whereby he obtained a double flank- 

 ing. The ditch, p, was constructed as before mentioned, but De Ville made it 

 pass round the place-of-arms, D, also, which he somewhat enlarged and called 

 a ravelin (demi-lune), opq, whereby he obtained yet another small place-of- 

 arms, n, in the salient angle. In the three systems hitherto described, all 

 the flanks have the fault of giving a too oblique defence of the ditch. 



4. Count Pagan divided his fortifications into great, medium, and small. 

 For the medium {pi. 48, fig. 8), the polygon side a b was 1080 feet. This 

 was bisected in c, a perpendicular erected at that point, cd z= 180 feet, and 

 the lines of defence h d o and a dp are drawn. The faces h h and «/ of 

 the bastions A and B were made 330 ft. and dm and dn each 192 ft. long. 

 Drawing, then, hm and fn, we have the flanks and the curtain C. Pagan 

 arranged three flanks, one behind the other, the foremost, im and gn, slightly 

 elevated above the bottom of the ditch, the middle, k and /, at the half 

 height, and the last at the full height of the bastions. The length of the 

 orillons h i and f g he determined, after De Ville, by the lines h g and a i, 

 intersecting each other at e, and the curtain received the breaks n o and 

 mp to make the second flanks longer. Sometimes there was disposed in 

 the bastions A and B an elevated parapet otq and p r s, called the cavalier. 

 F is the place of arms, and G the glacis. 



5. Vauban's first system (fig. 1) is applied upon a polygon side, a h, of 

 600 to 1080 feet. Jn the centre of this the perpendicular c ^ is erected, 

 made for the square =^\ ah, for the pentagon = ] ah, for the hexagon, &c., 

 z= \ ah, and the lines of defence h k and a I drawn through d, a, and h. 

 The faces a e and h h are made =^ ah, and from a and h as centres, circles 

 described with h e and af as radii : where these cut the opposite lines of 

 defence (at k and /) are the flank points ; the flanks, e k and //, and the 

 curtain C can now be drawn. Vauban also made orillons, but gave them 

 only one third the length of the flank. The first outwork which Vauban 

 added was the tenaille, which he established at 18 and 60 feet distance 



C33 



