Arfon, from the Welsh for "Facing Anglesey", refers to the southern shore of the Menai Strait, the part of mainland Wales closest to the island of Anglesey.
Iorwerth was apportioned the commotes of Arfon and Arllechwedd, with his seat at Dolwyddelan, with Maelgwn retaining Ynys Môn, and with Cynan receiving Meirionydd.
Other fortifications associated with Vortigern are at Arfon in Gwynedd, Bradford-on-Avon in Wiltshire, Carn Fadrun in Gwynedd, Clwyd in Powys, Llandysul in Dyfed, Old Carlisle in Cumberland, Old Sarum in Wiltshire, Rhaeadr Gwy in Powys, Snowdon, and Stonehenge in Wiltshire.