Norwich was a royal castle, and consequently always in the hands of the sheriff; it was never the property of the Bigods.[537] As the fable that extensive lands belonging to the monastery of Ely were held on the tenure of castle guard at Norwich _before the Conquest_ is repeated by all the local historians,[538] it is worth while to note that the charters of Henry I. setting the convent free from this service, make no allusion to any such ancient date for it,[539] and that the tenure of castle guard is completely unknown to the Anglo-Saxon laws. The area of the inner bailey is 3-1/4 acres, and that of the outer, 4-1/2 acres. The value of Norwich had greatly risen since the Conquest.[540] NOTTINGHAM (Fig. 22).--This important castle is not mentioned in Domesday Book, but the _Anglo-Saxon Chronicle_ says that William I. built the castle at Nottingham in 1067, on his way to repress the first insurrection in Yorkshire. Ordericus, repeating this statement, adds that he committed it to the keeping of William Peverel.[541] The castle was placed on a lofty headland at some distance from the Danish borough, and between the two arose the Norman borough which is mentioned in Domesday Book as the _novus burgus_. The two upper wards of the present castle probably represent William's plan. The upper ward forms a natural motte of rock, as it is 15 feet higher than the bailey attached to it, and has been separated from it by a ditch cut across the rocky headland, which can still be traced below the modern house which now stands on the motte. Such a site was not only treated as a motte, but was actually called by that name, as we read of the _mota_ of Nottingham Castle in the _Pipe Rolls_ of both John's and Richard I.'s reigns.