The Saxon Shore forts were built by the Romans in the third century AD as a defence against Saxon raiders. In Norfolk the ruins of the fort built at Burgh Castle (possibly Roman "Gariannonum"), guarding the estuary across from the island of Flegg, still remain, but there is now little remaining of the forts at Brancaster ("Branodunum") built on the north coast, and at Caister-on-Sea on the east coast, and close by to Burgh Castle. After the last of the armies of Rome left Britain in 410 AD, most of the visible remains of Roman Britain slowly disappeared.