in modern fortification, a huge mass of earth, usually faced with sods, sometimes with brick, and rarely with stone, standing out from a rampart of which it is a principal part. This is what, in the ancient fortification, was called a *bulwark*. Solid bastions are those which have the void space within them filled up entirely, and raised of an equal height with the rampart. Hollow bastions are those surrounded only with a rampart and parapet, having the space within unoccupied, where the ground is so low that no retrenchment can be made in the centre, in the event of the rampart being taken. *Flat bastion* is a bastion built in the middle of the curtain, when it is too long to be defended by the bastions at its extremes. *Cat bastion* is that which, instead of a point, has a re-entering angle. *Composed bastion* is when two sides of the interior polygon are very unequal, which makes the gorges also unequal. *Deformed bastion* is when the irregularity of the lines and angles puts the bastion out of shape; as when it wants a demigorge, one side of the interior polygon being too short. *Demi-bastion* is composed of one face only, with but one flank, and a demigorge. *Double bastion* is that which is raised on the plane of another bastion. *Regular bastion* is that which has its true proportion of faces, flanks, and gorges. See FORTIFICATION.