_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. _ef_C is the angle of _defence_. BC_f_ 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. [Illustration: FIG. 20.] 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 deg. 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 reduced as at G, it is called a _bonnet de pretre_. Such works were rarely used.) H. _Hornwork:_ Much used for gates, &c. I. _Crown-work._ K. _Crowned hornwork._ L. M. New forms of _tenaille_: (N.B.--These are the forms which ultimately retained the name.) N. New form of work called a _demi-lune lunettee_, the ravelin N being protected by two counterguards, O. P. _Re-entering places of arms._ Q. _Traverses._ R. _Salient places of arms._ S. _Places of arms_ without _traverses_. T. Orillon, to protect the flank V. X. A _double bastion_ or _cavalier_.