The art of fortification, or architecture militaire as vvell offensiue as defensiue, compiled & set forth, by Samuell Marolois revievved, augmented and corrected by Albert Girard mathematician: & translated out of French into English by Henry Hexam

The 17. Plate, and the 82. 83. Figure.

IF ye will not tye your selfe so precisely to this forme Octogonall, ye may make the towne much better by the meanes which wee will now speake of. Let first be drawne the lines D, D, and A, A. &c. right perpendiculars upon the midst of the curtaines N, M, and K, Y, of some 60 rod, or there abouts, then let there be made the perpendicular line infinite in the midst, and upon the curtaine D, E; in which ye haue the center of the circle, which makes the circle of all the figure, and suppose ye desire to make a forme regular of nine Bulwarks, whereof the angles flanked, are distant one from an other 80 rod, from the utmost end Q, shalbe made an arch, in such sort, that within the circuit thereof the distance N, P, is contained 9 times, which shall make the point of the center C, C. then upon the circumference of the said arch the said 9 points, being marked as they are noted here by the letters Q, R, S, T, V, X, Y, Z, &c ye shall make the angles interiour flanking, according to their forme, that ye may haue the angle flanked right, & that ye may the better make the angle flanking, or the tenaille pointed and small, which is accounted the best, as that skilfull, and diligent man M. Iohn Errard of Barleduke, Ingenier to the King of France hath obserued well, and to know how much the said angle flanking will make, ye must substract the halfe of the angle from the Bulwarke, or flanked from the halfe of the angle of the Polygone, the rest shalbe the angle flanking interiour. But if the angle of the Polygone be lesser then 150 degrees, which is the angle of a Dodecagone, ye shall then governe your selfe according to the table giuen before, takeing heede that the angle of the Polygone agreeth most with the angle to be fortified, and in its columne is found the angle flanking interiour, necessary to the said angle, by which ye may come to the angle of the tenaille, & seing in this exemple wee haue set downe the distāce frō angle to angle, as wel of the Pentag. as of the towne 80 rod, wee wil set downe upon the lines, which make the tenailles 2 equall parts, & from the said 2 parts in the line which formeth the angle flanking, a parallell line being drawne to that of 80 rod, & placed upō the 3 equall parts, a privie line infinite, must be drawne through the said 3 point, & through the angle, and where the same comes to cutt the other side of the tenaille in the point O, ye shall haue the shoulder, through which the line A, B, being drawne, makeing the angle forming the flanke 40 degrees, ye shall haue the center of the Bulwarks justas wee haue taught heretofore in the 10 & 11 plates. If the Castle had bin made with foure angles, the construction would haue ben the

same, and if the lines D, D, Q, and A, A, &c. had bene somewhat more then 60 rod, the forme would haue bene better, for though we haue made the lines of defence, to be 60 rod in the former Fortresses, there is an other consideration in this present building; in regard the Bulwarkes Q, &c. advance themselues towards the angles Q, &c. from whence the said curtaines Q, E, E. & B, B &c. maye be sufficiently de∣fended, when they doe not exceede aboue 70 rod, the moates, covert wayes, false∣brayes and other workes, must be made in that forme as we haue sett them downe before in the 16. plate.