OXFORD (Fig. 25).--This castle was built in 1071 by Robert d'Oilgi (or d'Oilly), a Norman who received large estates in Oxfordshire.[557] Oxford was a burgus in Saxon times, and is one of those mentioned in the _Burghal Hidage_. Domesday tells us that the king has twenty mural mansions there, which had belonged to Algar, Earl of Mercia, and that they were called mural mansions because their owners had to repair the city wall at the king's behest, a regulation probably as old as the days of Alfred. The Norman castle was placed outside the town walls, but near the river, from which its trenches were fed.[558] It was without doubt a motte-and-bailey castle; the motte still remains, and the accompanying bird's-eye view by David Loggan, 1675, shows that the later stone walls of the bailey stood on the earthen banks of D'Oilly's castle. The site is now occupied by a gaol. On the line of the walls rises the ancient tower of St George's Church, which so much resembles an early Norman keep that we might think it was intended for one, if the Osney chronicler had not expressly told us that the church was founded two years after the castle.[559] It is evident that the design was to make the church tower work as a mural tower, a combination of piety and worldly wisdom quite in accord with what the chronicler tells us of the character of Roger d'Oilly. Henry II. spent some £260 on this castle between the years 1165 and 1173, the houses in the keep, and the well being specially mentioned. We may presume that he built with stone the decagonal [shell?] keep on the motte, whose foundations were discovered at the end of the 18th century.[560] There is still in the heart of the motte a well in a very remarkable well chamber, the masonry of which may be of his time. The area of the bailey appears to have been 3 acres. The value of the city of Oxford had trebled at the time of the Domesday Survey.[561] In the treaty between Stephen and Henry in 1153 the whole castle of Oxford is spoken of as the "Mota" of Oxford.[562]