FORTIFICATION. 155 



flanking them, was first abandoned in the sixteenth century, and it is 

 believed that the Italians were the first to substitute bastions in place of 

 towers. The works of earlier military engineers were improved upon by 

 Vauban, and his system again by Cormontaigne in 1716. 



Before we proceed further, we must explain some technical terms which 

 have not been employed in treating of field fortification. The foundation 

 of every fortification is the regular or irregular polygon, which is drawn 

 around the place to be fortified, and whose side must not be greater than 

 the effective range of small arms, as otherwise the flanking will be insuf- 

 ficient. By the breaking of these polygon sides into any figure soever 

 arises the system of fortification. The exterior polygon is that which is 

 drawn through the vertices of the salient angles ; the interior polygon 

 unites the vertices of the re-entering angles. The fine which bisects an 

 angle is its capital, and the portion of the fortification lying between two 

 adjacent capitals is called a front of attack. The construction must take 

 place always according to the exterior polygon, as otherwise it could not 

 be determined where the bastion points fall. The angles made by the 

 faces are called bastion salients ; angles which the faces make with the 

 flanks are shoulder angles, and the angles of the curtains and flanks are 

 flank or curtain angles. If a part of the flank projects forward, to cover 

 the rest lying back of it, this forms an orillon. The line from one flank to 

 the opposite bastion salient is called the line of defence, and its length must 

 not exceed the effective range of small arms. The rampart immediately 

 surrounding the place to be fortified is called the enceinte, or body of the 

 place, and the line along which the defenders stand is the magistral. All 

 works lying in front of the enceinte, but within the covered way, are called 

 outworks ; if outside of the latter they are detached works. 



The chief part of every fortification is the rampart, which consists of the 

 parapet and the terreplein lying behind it, on which the artillery and 

 defenders find room for position and movement. The breadth of this was 

 formerly taken at 24 feet, but in later times it has gone up even to 42 feet. 

 The thickness of the parapets proper must be from 18 to 20 feet, their 

 height 7^ feet, and their slopes governed by the natural fall of the earth ; 

 in bad soil they must be even greater (H of the height). The communica- 

 tion between the terreplein and the interior of the place is secured by 

 means of ramps {pi. 48, fig. 42), which are cut in the slope of the terre- 

 plein. Of the outworks, the ditch which surrounds every fortified place is 

 the first. The ditch may be either dry or wet ; there are dry ditches, 

 however, which can at times be put under water. If the bottom of a dry 

 ditch is moist, a canal is established in the middle of it, the cunette, to 

 carry oflf the water, and over this small bridges are laid. Ditches which 

 can be inundated obtain their water usually from some river running by 

 the place, and are then provided with sluices. These are stone dams 

 (Batardeaux), which run across the ditch, and have a sluice in the centre, 

 placed in a tower which is accessible only from the fortification. Fig. 39 

 is the elevation of such a sluice-tower ; fig. 40, the section of another ; and 

 fig. 41, the arched passage for the water. In the ditch lies, in front of the 



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