The late Romano-British population seem to have been mostly Christian by the Sub-Roman period. The Great Conspiracy in the 360s and increased raiding around the time of the Roman withdrawal from Britain saw some enslaved. Later medieval legends concerning the conversion of the island under King Lucius or from a mission by St Philip or Joseph of Arimathea have been discredited; they are alleged to be "pious forgeries" introduced in attempts to establish independence or seniority in the ecclesiastical hierarchy formalised following the Norman conquest of England and Wales. The first archaeological evidence and credible records showing a community large enough to maintain churches and bishops date to the 3rd and 4th centuries. These more formal organisational structures arose from materially modest beginnings: the British delegation to the 353 Council of Rimini had to beg for financial assistance from its fellows in order to return home. The Saxon invasions of Britain destroyed most of the formal church structures in the east of Britain as they progressed, replacing it with a form of Germanic polytheism. There seems to have been a lull in the Saxon westward expansion traditionally attributed to the Battle of Badon but, following the arrival of Justinian's Plague around 547, the expansion resumed. By the time Cornwall was subjugated by Wessex at Hingston Down in 838, however, it was largely left to its native people and practices which remained inherently Christian in character and St Piran's Oratory is dated to the 6th century, making it one of the oldest extant Christian sites in Britain.