Only five years after this, in 1070, the Conqueror held his court on the hill of what was then New Windsor. In the Domesday survey of 1086 a castle there is mentioned, but what it was we cannot be sure, and there are no visible remains of it. The position had struck and pleased the Conqueror as soldier and hunter, for he not only fortified the hill but recovered, to form part of a forest, some neighbouring lands which the Confessor had given to his Abbey of Westminster. The early Norman castles in England and Normandy were of timber, and consisted of a ditched and palisaded mound and a court, or several courts, also ditched and if possible moated with water. Under William the castle tended to become a high stone keep of rectangular form, with towers at the corners, depending for its strength upon the thickness of its own walls, not on a series of outer fortifications. In 1095 Windsor was used as a prison for Robert de Mowbray, Earl of Northumberland, by the second William, but Old Windsor was still at times a royal residence while the new castle was being built. Henry I added "many fair buildings", including a chapel, and held his court there for the first time at Whitsuntide in 1110. At Windsor Henry married his second queen, Alice the Fair, and there also he kept Whitsuntide when David of Scotland and the English barons swore fealty to his daughter, the Empress Maud. At the time of the peace between Henry and Stephen the Castle was the second fortress in the kingdom, and its castellan, like those of London, Oxford, Lincoln, and Southampton, gave hostages for its surrender to Henry in the event of Stephen's death.