BASTION, in fortification, is one of the principal defense-works in a fortified place. It is a kind of tower, very broad in relation to its height. The plain wall, called the curtain, which often surrounds a fortified town, is usually a polygon of many sides; and in that case, bastions occupy all, or nearly all, the salient angles. Bastions are mostly five•sided: the two outermost sides are the faces, in an angle towards the enemy; the two on either side of these are the flanks, meeting two curtains or portions of wall; and the fifth side, open to the interior of the fortified place, is the gorge. Bastions may be regarded as projections, which enable the defenders to watch the approach of the enemy to the foot of the wall, and to frustrate them by a flanking fire. Taking the aver age range of modern ordnance and muskets as a basis, engineers decide on a distance of BOO to 400 yards between B. and B.; but if Armstrong or Napoleon guns, and Martini Ilmry or 31inie rites, should hereafter be employed in attacking and defending fortified places, these figures will probably need modification. The length of each face and flank of a B. is so regulated, that two bastions can defend each other and the por tion of wall. This principle was partly acted upon in the middle ages; but sonic of the Italian military engineers of the 16th c. first constructed the B. proper. The main sub
stance of a B. is an immense mound of earth, capable of supporting heavy guns, and of receiving the fire of the enemy; but it is faced and strengthened in many parts with Nick and stone. The top is broad enough to allow room for the large guns, and for Infantry and artillery soldiers. A hollow B. has the space within it kept down to the level of the town or natural ground; but a solid B., filled up to the top with firm mate rials, is considered to be the best defensive construction. Vauban, the great French engineer, devised the plan of having large detached bastionsopposite the chief angles of the place, with a ditch behind each; a tower or small B. being placed at the real angle of the wall behind. This was intended to enable the besieged to hold out for some time, even after the great bastions were taken.
The relation which bastions bear to the general system of attack and defense, is noticed under FORTIFICATION and SIEGE; while various details on the subject will be found under BATTERY, CASEMATE, CURTAIN, DITCH, EMBRASURE, ESCARP, PARAPET, RasicAirr, etc. In woodcuts illustrating many of these articles, the relative position of the B. will be better shown than by any diagram in this place.