Bastion

A distinct sub-division of the enceinte of a fortification consisting of two faces forming a salient angle and two flanks. Bastions were usually, but not always, traced in such a way that they joined the extremities of two collateral fronts of fortification with the salient (flanked) angle anchored on the vertex of one of the angles of the fortified polygon. Bastions were an integral element of the flanked disposition: each bastion flank could cover the flanked angle of the next bastion and cross its fire with the curtain, flank of the next bastion, and face of the next bastion to defend both the main ditch and crest of the counterscarp.

Typical Elements of Bastions
Exhibited as Lines and Angles Traced on an Irregular Polygon of Fortification
KEBFL	A Bastion
AB, BC	Exterior sides of the Polygon of Fortification
AD, EB, BF, GC	Bastion Faces
DH, EK, FL, GM	Bastion Flanks
HK, LM	Curtains
EBF	Flanked Angle (Salient of the Bastion)
D, E, F, G	Shoulders of the Bastions
BEK, BFL	Angles of the Bastion Shoulders
DHK, EKH, FLM, GML	Angles of the Curtains
BN	Capital of the Bastion
O	Center of the Bastion
KL	Gorge of the Bastion
KN, LN	Demi-Gorges of the Bastion

There were six basic types of bastions: demi-bastions, empty bastions, full bastions, flat bastions, detached bastions, and tower bastions. A Demi-Bastion, also called a half-bastion, was a salient element of a fortification that included the typical bastion trace of face and flank on one side of the capital of the salient angle and a straight line of rampart or parapet that was directed toward the rear on the opposite side of the capital.

An Empty Bastion had its interior space within the limits of the gorge, faces, and flanks on a level with the parade or terre-parade of the fortification. In this type of bastion the parade wall or slope of the rampart terre-plein ran parallel to the magistral line of the rampart or interior crest of the parapet, leaving the space enclosed by the gorge, faces, and flanks empty. A Full Bastion, on the other hand, had its interior space raised to the level of the terre-plein of the rampart. The interior space of this type of bastion was enclosed by a parade wall or ramp of the terre-plein of the rampart which followed the line of the gorge of the bastion and was usually filled with earth.

A Flat Bastion was traced with its flanked angle at or near the mid-point of the exterior side of the polygon of fortification. Flat bastions were used to produce flanking defense when the exterior side of the fortified polygon was exceptional long and bastions at the angles of the polygon would be too far apart to effective defend each other's flanked angles. A detached bastion was separated (that is, detached) from the curtains on its flanks by coupures or a ditch that followed the line of the bastion gorge and broke the continuity of the rampart of the enceinte. A Tower Bastion, unlike the other types, was constructed as a hollow masonry structure with embrasured casemates on the flanks or faces and interior casemates and passageways. This type of bastion was generally much smaller than other bastion types.

January, 2003

August, 2005