This constitutes the main walls of a fortification, generally referring to a continuous wall that surrounds/defends a central hub, such as a town or keep. It includes the gate houses, towers and the like. The enceinte is usually huge and thick. During the Seige of St Elmo on the island of Malta during the Turkish invasion of 1565 the enceinte withstood weeks of continuous bombardment from the Turkish guns before the walls were reduced to little more than ridge-like mounds of rubble and dust.
Its here, famously, that a wounded Knight of St. John mounted the walls in his chair to fight off the Turk, who in turn withstood withering fire during the attack.