These forts or strong points, as they are sometimes called, usually round or square, but which may be any shape best suited to the condition of the country in which they are placed, are generally from 100 to 300 yards behind the fire-trenches and supplementary to the support trenches. Each of these strong points contains a permanent garrison of firing troops, strongly protected with barbed wiring and sandbag revetments, and well supplied with ammunition, food and water, to enable them to withstand heavy attacks. During an attack they are used to give overhead covering fire, and for the control of ammunition and other supplies to be sent on to the firing line. It is a general rule that if the enemy take a fire line the garrison of these supporting points must hold out and remain a thorn in the enemy’s side until the last man of the garrison is killed.