DECURIO, in Roman military history, a commander of ten men in the army, or chief of a decury.
DECURY, ten Roman soldiers ranged under one chief, or leader, called the Decurio.
DEEP, troops are told off in ranks of two, or 3 deep, and on some occasions in 4 or more.
DEFAULTER. See [Deserter].
DEFEAT, the overthrow of an army.
DEFECTION. See [Mutiny].
DEFENCE, in fortification, consists of all sorts of works that cover and defend the opposite posts; as flanks, parapets, casemates, and fausse-brays. It is almost impossible to fix the miner to the face of a bastion, till the defences of the opposite one are ruined; that is, till the parapet of its flank is beaten down, and the cannon, in all parts that can fire upon that face which is attacked, is dismounted. See [Fortification].
Active Defence, generally considered, means every species of offensive operation which is resorted to by the besieged, to annoy the besiegers. Such for instance, is the discharge of heavy ordnance from the walls, the emission of shells, and the firing of musquetry. A mass of water may likewise be understood to mean active defence, provided it can be increased according to the exigency of the service, and be suddenly made to overflow the outworks, or entrenchments of the besieging enemy. Mines which are carried beyond the fortifications may likewise be included under this head.
Passive Defence is chiefly confined to inundations, and is effected by letting out water in such a manner, that the level ground which lies round a fortified town or place may be entirely overflowed and become an inert stagnant pool. Mere submersion is, in fact, the distinguishing character of this species of defence, which does not afford any other movement than what naturally arises from the greater or lesser elevation of the waters, without the means of urging them beyond a given point.
Distant Defence, consists in being able to interrupt the enemy’s movements by circuitous inundations; to inundate, for instance, a bridge, when a convoy is passing, or to insulate batteries, the heads of saps or lodgments which have been made in the covert way is to act upon a distant defence. By this species of defence an enemy’s communications may be perpetually intercepted, and his approaches so obstructed as to force him to leave dangerous intervals.