Lancaster was founded by the Romans and a fort was built on the slope below the site of the present castle. There is also some evidence that the adjacent estuary of the River Luna may have been used by the Imperial Fleet, the Classis Britannicum, probably as a supply port for the forts in the Lakes and the western end of Hadrian's Wall.
After the Roman withdrawal the land fell back into barbarism, and even by the time of Domeday the town represented a bastion against a wild and uncivilised North. As such, and with the border with Scotland becoming established and then moving north and south with wars and raids, Lancaster became one of the English crown's main bulwarks. A castle was built here, and the area to the south became Lancashire, stretching down to the more placid lands of Cheshire, and east to the Pennine mountain chain.