Derby was a Danish stronghold in 917. The line of the Medieval defences remain uncertain but are recorded in Medieval documents.
There may have been a Saxon village on the site of Derby after the Romans left. However the Danes founded the town of Derby about 873 AD after they invaded England. They created a fortified settlement at Derby. It was an easy place to fortify. To the east the river Derwent protected it. To the east [sic west is meant] and south a tributary of the Derwent protected Derby. All the Danes had to do was to fortify the northern approach between the two rivers. They dug a ditch and erected an earth bank with a wooden palisade on top. (Lambert)
During remediation works in March 2007 the remains of a large ditch feature were identified. The fill of the ditch, locally more than 2m in depth, produced a range of medieval pottery. Preliminary analysis suggests the lower fill levels date to the 12th century. It is possible that this is the northern medieval town ditch for which there are 13th century documentary references. If correct, this is the first secure sighting of the town ditch and is important in understanding the layout of medieval Derby. (Derbyshire HER ref. Kinsley; Myers)
Lambert statement was unsupported by evidence but he was not unreasonable in expecting the main artificial line of defences to be to the north of the medieval town. A line near King Street is not unreasonable.