The earliest Iron Age defensive site at Colchester is the Pitchbury Ramparts earthwork north of the town between West Bergholt and Great Horkesley. The main earthwork defences of the Brythonic Celtic oppidum of "Camulodunon" were built later, beginning in the 1st century BC but most date from the 1st century AD. They are considered the most extensive of their kind in Britain. The defences consist of lines of ditches and ramparts, possibly palisaded with gateways, that mostly run parallel to each other in a north–south direction. The Iron Age settlement was protected by rivers on three sides, with the River Colne bounding the site to the north and east, and the Roman River valley forming the southern boundary; the earthworks were mostly designed to close off the western gap between these two river valleys. Other earthworks close off eastern parts of the settlement. These earthworks gave the oppidum its Brythonic Celtic name – "Camulodunon" meant "the stronghold of Camulus", the British god of war. Together they enclose an area of , much larger than the area enclosed by the Iron Age defences at Wheathampstead ().