The earliest Welsh genealogies give Maximus (referred to as Macsen/Maxen Wledig, or Emperor Maximus) the role of founding father of the dynasties of several medieval Welsh kingdoms, including those of Powys and Gwent [REF].
The ninth century Historia Brittonum gives another account of Maximus and assigns him an important role: The seventh emperor was Maximianus, He withdrew from Britain with all its military force, slew Gratianus the king of the Romans, and obtained the sovereignty of all Europe.