 So extensive have the changes to this landscape been that what little evidence there is of man's presence before the ice came has inevitably shown signs of transportation here by water and reveals nothing specifically local.Likewise, later evidence of occupation, even since the arrival of the Romans, may lie next to the original banks of the Brent but have been buried under centuries of silt.Some of the earliest written references to the Thames () occur in Julius Caesar's account of his second expedition to Britain in 54 BC, when the Thames presented a major obstacle and he encountered the Iron Age Belgic tribes the Catuvellauni and the Atrebates along the river.