following the roman withdrawal from britain around  410, the cornovians seem to have divided into pengwern and powys. the minor magonsæte sub-kingdom also emerged in the area in the interlude between powysian and mercian rule. viroconium may have served as the early post-roman capital of powys prior to its removal to mathrafal sometime before 717, following famine and plague in the area. the city has been variously identified with the and which appeared in the 9th-century "history of the britons"s list of the 28 cities of britain.