Page:EB1911 - Volume 10.djvu/707

Rh Flanks retired, casemated or open, or sometimes in several tiers were proposed in infinite variety.

Thus, while in the early part of the 16th century the actual modification of existing defences was proceeding very slowly on account of the expense involved, the era of theoretical “systems” had begun, based on the mutual relations of flank and face. These can be grouped under three heads as follows:—

1. The crémaillère or indented trace: Faces and flanks succeeding each other in regular order (fig. 15).

2. The tenaille trace: Flanks back to back between the faces (fig. 16). The development of the flanks in this case gives us the star trace (fig. 17).

3. The bastioned trace: Flanks facing each other and connected by curtains (fig. 18).

In comparing these three traces it will be observed that unless casemates are used the flanking in the first two is incomplete. Guns on the ramparts of the faces cannot defend the flanks, and therefore there are “dead” angles in the ditch. In the bastioned trace there is no “dead” ground, provided the flanks are so far apart that a shot from the rampart of a flank can reach the ditch at the centre of the curtain.

Here was therefore the parting of the ways. For those who objected to casemate fire, the bastioned trace was the way of salvation. They were soon in the majority; perhaps because the symmetry and completeness of the idea

captivated the imagination. At all events the bastioned trace, once fairly developed, held the field in one form or another practically without a rival until near the end of the 18th century. The Italian engineers, who were supreme throughout most of the 16th century, started it; the French, who took the lead in the following century, developed it, and officially never deserted it until late in the 19th century, when the increasing power of artillery made enceintes of secondary importance.

It will be useful at this point to go forward a little, with a couple of explanatory figures, in order to get a grasp of the component parts of the bastioned trace as ultimately developed, and of its outworks.

In fig. 19 ABCD represents part of an imaginary line drawn round the place to be fortified, forming a polygon, regular or irregular.

ABC is an exterior angle or angle of the polygon.

BC is an exterior side.

zz is an interior side.

abcdefghijk is the trace of the enceinte.

bcdef is a bastion.

zdef is a demi-bastion.

de is a face of the bastion.

ef is a flank of the bastion.

fg is the curtain.

bf is the gorge.

(Two demi-bastions with the connecting curtain make the bastioned front, defghi.)

zd bisecting the exterior angle ABC is the capital of the bastion.

xy is the perpendicular, the proportionate length of which to the exterior side BC (usually about one-sixth) is an important element of the trace.

efC is the angle of defence.

BCf is the diminished angle.

cde is the flanked angle or salient angle of the bastion.

e is the shoulder of the bastion.

def is the angle of the shoulder.

efg is the angle of the flank.

The line of the escarp is called the magistral line since it regulates the trace. When plans of fortifications are given without much detail, this line, with that of the counterscarp and the crest of the parapet, are often the only ones shown,—the crest of the parapet, as being the most important line, whence the fire proceeds, being usually emphasized by a thick black line.

Fig. 20, reproduced from a French engraving of 1705, shows an imaginary place fortified as a hexagon with bastions and all the different kinds of outworks then in use. The following is the explanation of its figuring and lettering.

1. Flat bastion: Placed in the middle of a curtain when the lines of defence were too long for musketry range.

2. Demi-bastion: Used generally on the bank of a river.

3. Tenaille bastion: Used when the flanked angle is too acute; that is, less than 70°.

4. Redans: Used along the bank of a river, or when the parapet of the covered way can be taken in reverse from the front.

A, B. Ravelins.

C. Demi-lunes: So called from the shape of the gorge. They differ from the ravelins in being placed in front of the bastions instead of the curtains.

D. Counter-guards: Used instead of demi-lunes, which were then going out of fashion.

E. Simple tenaille.

F.Double tenaille (see L and M).

(If the tenaille E is reduced in width towards the gorge, as shown alternatively, it is called a swallow-tail. If the double tenaille is