The presence of the double castle at York has been a great temptation to those who would identify the castle with the _burh_. The fortification of both banks of the river is, on the face of it, so like the system adopted by Edward the Elder, that the York castles have been often quoted as _burhs_ of Edward the Elder’s date, and it has been concluded that similar earthworks must have existed at Nottingham, Stamford, and so on. This idea is quite untenable. Had William followed the example of Edward and Æthelflæd, he would simply have repaired or renewed the defences of the two divisions of the _burh_ at York.[47] But what he had to provide against was the spirit of rebellion in the _burh_ itself, as well as the possible use of the water-way by Danish pirates. Which castle he first founded at York we do not know. On the tongue of land which runs out between the Ouse and Foss, outside the _burh_, and between it and the river approach to the city, one castle rose. The other, a fortress known in later times as the Old Baile, was possibly from the beginning partly within the ramparts of the southern _burh_. Later, at any rate, the city wall was built across the foot of the outer side of its mount, and enclosed the bailey on two sides. Elsewhere, the distinction between William’s castles and the _burhs_ within which they rose is very noticeable. At Lincoln the castle filled up an angle of the Roman city. At Cambridge, the mount rises on the highest point of a large enclosure—the original _burh_—surrounded by earthworks of early date. Further, if any documentary proof is needed of anything so self-evident as the distinct nature of the castle and the _burh_, Domesday is clear upon the point. Apart from the evidence which it gives us with respect to the borough or _burh_, it speaks in one place of the _burgum circa castellum_—the _burh_ about the castle. The case in point is the castle of Tutbury in Staffordshire, a fine example of the mount-and-bailey stronghold.[48] One important feature here is that the castle, very large in area, and with a ditch of great depth on two sides, was apparently raised on the site of an early hill-fort or _burh_, and that the actual _burh_ about the castle, the modern village of Tutbury, has grown up under its protection on the slope towards the Dove. [Illustration: Berkhampstead]