In order to secure the subjection of his new subjects, the Conqueror did not neglect the important means which the erection of castles or fortresses presented. Amongst others, he either built, or caused his chief vassals to build, those of Pevensey, Hastings, and the White Tower of London. The castles, or stone-built fortresses of England, previous to the Conquest, were few and inconsiderable. Those erected by the Romans had fallen into ruin; and although Alfred the Great had strengthened the defences of the country by upwards of fifty towers of defence, they had not been kept up by his successors; and to this neglect the speedy reduction of the country to the Norman yoke may, in a large measure, be attributed. There were no long and wearisome sieges to undertake; no position capable of holding an army in check for any length of time: all was left to the chance of an open battle. At the period previous to the Conquest, the castles and places of strength were chiefly of wood. William determined to alter this, and speedily commenced the erection of his strongholds, and in process of time the great feudal barons followed his example. In order to afford an idea of these structures, we shall, as briefly as possible, give a general idea of a Norman fortress or castle. It consisted of an enclosure, varying, according to the importance of its position, of from five to ten acres of land, and, where circumstances rendered it possible, was surrounded by a moat or artificial canal, on the edge of which was a strong wall enclosing a second wall. Between these was the first ballium, or outer court. Within the second wall, which surrounded the keep, or great tower, were storehouses for the garrison, and other offices, as well as lodgings for the troops. In the centre of the interior space stood the citadel, keep, or master tower, in which resided the governor, or feudal possessor; in his absence, the castellan inhabited it, exercising the same authority as his chief. This last edifice was generally erected on an artificial or natural mound. It contained the state apartments, together with the domestic offices, and, in the centre, below the foundations, the dungeons for prisoners of war and other captives, such as felons, who had fallen under the jurisdiction of the lord or governor. In many instances there were secret means of access to these prisons by narrow passages contrived in the walls. In advance of the moat stood the barbican, or outward defence, with a watch-tower, communicating with the interior by means of a drawbridge, which drew up from within, so as to be under the direction of the sentinel or guard. The entrance to the ballium, or outward court, was still further secured by a strong gate, defended by a portcullis, to be raised or lowered as occasion required, by means of strong iron chains and pulleys. The walls were further protected by battlements, perforated by loopholes, through which arrows could be discharged, and