Gildas, a British monk, wrote 'The Ruin of Britain', the only near-contemporary source for the collapse of Roman Britain and the arrival of the Anglo-Saxons ... those of the Celtic church ...

Near the end of Roman rule, Britain was being attacked by the Picts and Scots from the north, and the Anglo-Saxons from the sea. The Romans built forts to defend the coast and Hadrian's wall ...