CITADEL, is also a small fortification, consisting of four, five, or six sides, with bastions, by which it is distinguished from a castle, and usually joined to towns, and sometimes erected on commanding eminences within them.
Citadels may be either square, rectangular, pentagonal, hexagonal, or, indeed, of any figure ; but the pentagonal is most commonly adopted. The hexagonal is generally con sidered as to large, and requiring too great an expenditure for the advantages to be derived from it ; and the quadrangular is incapable of making a sufficient defence. Citadels are also sometimes made in the form of a star fort.
The exterior sides of the citadel, when its plan is regular, arc generally, each about 150 toises, or fathoms; but this extension may be varied according to circumstances.
When the citadel is erected on a hill, or eminence, within the fortifications of the place, it is well calculated to keep the inhabitants in awe, if the garrison he sufficiently provided ; but it is of little use against an enemy, w hen once in posses sion of the town itself.
The citadel will require a stronger fortification than the town, to prevent its being attacked first by the enemy, who, getting possession of it, will scum become masters of the town.
A citadel has, for the most part, two gates, the one for com municating n ith the town, and the other w ith the country ; the gate communicating with the town, is used in case of an insurrection or sedition, or after the town has capitulated, for the garrison to retire into the citadel ; the other gate, which communicates with the country, is for receiving assistance and succours when placed under extremities. The citadel generally takes up two sides of the fortification of the parts which adjoin to it, and be so constructed that the ditch of the place may be defended as directly as possible, either by the faces of its bastions, or by ravelins, that the enemy may have no greater advantage in attacking in one place than they would have in another. It may be fitrther observed, that in an extensive fortified city. a citadel may be formed by uniting two adjoining bastions, by a good retrenchment, with flanking defences: the expense of making such is very compared with that of adding another fortification to the place.