FORTIFICATION. 497 



height of the covert way, the glacis (G) slopes off to the natural 

 ground on the exterior. The salient, and reentering parts of the 

 covert way, are enlarged, to form places of arms, (R, and S), which 

 are separated from the rest of the covert way by traverses, (t, t) ; to 

 ward off the fire of the enemy, and enable these portions to be de- 

 fended separately. A small work called the tenaille, (T), is some- 

 times placed in the main-ditch, in front of the curtain, to shelter this 

 part from the enemy. The postern, or main entrance to the fort, 

 leads through the middle of the curtain : and there is a passage 

 through the tenaille, to the demilune, protected by a double capon- 

 nier, or kind of glacis, (C), on each side of it, sloping off into the 

 ditch. 



3. On the Mack and Defence of Places, or the operations 

 during a siege, by both the parties concerned, we must here be ex- 

 tremely brief. The besiegers begin by investing or surrounding the 

 fort, with a very superior force ; protecting themselves from the 

 sorties of the garrison by lines of circumvallation ; and, if neces- 

 sary, constructing lines of count ervallation, to protect themselves 

 from any exterior army coming to relieve the garrison ; which latter 

 is thus cut off from all extraneous supplies or assistance. The 

 enemy next advances near to the fort, on what he supposes to be its 

 weakest side ; and there, under cover of the night, digs a trench, to 

 shelter his men, called the first parallel. This trench is often more 

 than a mile long ; and extends circularly around that side of the fort, 

 at a distance of 600 or 800 yards. A strong guard is then placed in 

 it, to defend the sappers ; who now dig trenches from it, advancing 

 towards the fort, called boyaux. These trenches proceed obliquely, 

 in a zigzag line towards the fort, to avoid being enfiladed by its fires. 



Meanwhile, the besiegers are erecting batteries, at intervals along 

 the first parallel, to destroy or silence the guns of the fort, before thejr 

 venture to approach nearer. The ricochet fires, in which the ball 

 strikes so obliquely, as to rebound several times successively, are the 

 most effective for this purpose. When the boyaux are extended 

 nearly halfway from the first parallel to the fort, a second parallel is 

 dug, to which the guards are then advanced, while the sappers advance 

 still farther. In this manner, the third or fourth parallel will bring 

 them close to the crest of the glacis ; along which they will next, by 

 sapping, or by storm, dig a trench, in which to defend themselves, 

 and erect new batteries to make breaches in the walls of the fort. 

 The digging of this trench, is called crowning the covert way ; from 

 which, the garrison will then be obliged to retreat to the demilune. 

 As soon as a breach is made in the scarp of the demilune, and a gal- 

 lery dug by which to descend into its ditch, the besiegers will storm 

 this outwork, climbing up over the ruins, and entrenching themselves 

 therein ; and they will then proceed in the same manner to carry the 

 main work, unless it capitulate, or be relieved by an external force. 



The providing of means for passing armies over rivers, is a com- 

 mon duty of the engineers and artillery. Where ordinary bridges 

 are not, or cannot be constructed, and common boats cannot be pro- 

 cured, pontoons are occasionally used ; which are flat bottomed boats 

 of a prescribed shape and size ; such as are usually transported, in 

 63 2 T2 



