Southampton's town walls are a sequence of defensive structures built around the town in southern England. Although earlier Roman and Anglo-Saxon settlements around Southampton had been fortified with walls or ditches, the later walls originate with the move of the town to the current site in the 10th century. This new town was defended by banks, ditches and the natural curve of the river and coastline. The Normans built a castle in Southampton but made no attempts to improve the wider defences of the town until the early 13th century, when Southampton's growing prosperity as a trading centre and conflict with France encouraged the construction of a number of gatehouses and stone walls to the north and east sides of the settlement.