 These and the ditches, built during the Seven Years' War (1756–63), became known as the "Chatham lines" and were entered by four gateways with bridges.The fortifications were designed in 1755 by Captain John Peter Desmaretze of the Board of Ordnance and consisted of a earthwork ditch and a parapet.In 1757, an infantry barracks (for a troop garrison) was built to man the defences.