Fig. 80.
In proportion to the length of the trajectory, therefore, the defence must remove its defensive arrangement from the centre of the place.
Fig. 81.
If each front of Vauban's defence was about four hundred yards in length, it ought to be from thirteen to fourteen thousand yards now ([Fig. 81]). That is to say, the side of the hexagon which was four hundred yards—i.e., from one salient of a bastion to another—should be fourteen hundred yards. Let A be the main body of the fortress—on a plain suppose; forts will be erected at B and C, the zone of action of each of these works being eight thousand yards, they will protect each other and cross their fires without the possibility of their projectiles falling into the fortress if any of them should be in the power of the enemy.
Fig. 82.
[Fig. 82] presents the block plan of each of those forts B and C, to whose interior arrangements we shall return. But by this excessive lengthening of the capitals, the forts B ([Fig. 81]), may be swept along the whole extent of the arc of a circle a b (more than the third of the circumference); they occupy the points of a triangle, and if one of them were taken the enemy would be able to batter two of the forts C. It is therefore necessary, with an extended radius, to multiply the defences, and to enable them to protect each other in a more effective manner. This is the method indicated in [Fig. 83].