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).