Any of the inhabitants of Gaul north of the Sequana and Matrona (Seine and Marne) rivers of mixed Celtic and Germanic origin, first described by Julius Caesar in mid-first century BC. Their origins on the continent can be traced back to the La Tène period in the 5th century BC and evidence suggests that the Romans penetrated into those areas about 150 BC. In Caesar's day, they held much of Belgium and parts of northern France and southeast England. The Belgae of Gaul formed a coalition against Caesar after his first Gallic campaign but were subdued the following year (57 BC). During the first half of the 1st century BC, Belgae from the Marne district had crossed to Britain and had formed the kingdom that in 55 BC was ruled by Cassivellaunus. After further Gallic victories (54-51 BC) by Caesar, other settlers took refuge across the Channel, and Belgic culture spread to most of lowland Britain. The three most important Belgic kingdoms, identified by their coinage, were centered at Colchester, St. Albans, and Silchester. Archaeologically, the Belgae can be identified with the bearers of the Aylesford-Swarling culture, otherwise known as Iron Age C. Coinage, the heavy plow, and the potter's wheel were introduced by the Belgae. They lived in large fortified settlements called oppida and amphorae and Italian bronze vessels have been found in their richly furnished tombs.