Evidence indicates a Roman settlement with a farmstead, a garrison, a burial ground, and the operation of a large salt-making industry. A Roman road indicates that they might have been transporting the salt to Chelmsford and Colchester.
Over 200 Red Hills have been found near saltings which indicate salt mining activity. At the time the island was about 12 feet higher than it is today although was prone to periodic flooding. The sea defences were not built until the 17 century.
see Wikipedia
see Canvey Island