 He is given as the ancestor of a Welsh king on the Pillar of Eliseg, erected nearly 500 years after he left Britain, and he figures in lists of the Fifteen Tribes of Wales.The 400-year period following the collapse of Roman rule is the most difficult to interpret in the history of Wales.After the Roman departure from Britain in AD 410, much of the lowlands of Britain to the east and south-east was overrun by various Germanic peoples.