Arvor (British: Arvor, Lyonnaise: Armorique) is a historic and cultural region in Lyonesse, comprising the westernmost peninsula between the Gallic Channel, the Bay of Biscay and the River Loire. The name derives ultimately from the Old Gaulish "Aremorika", meaning "Place by the Sea", and was being used to specifically denote the present-day area by the early Roman period. Arvor has always had strong connections with Albion to the north, and extensive British immigration during the 5th and 6th centuries has ensured that a dialect of the British language is still the majority tongue to this day.
The region formerly comprised an independent kingdom. It was established in 630 by Iudhel ap Hywel who united the British kingdoms of Broerech and Dyfnaint Newydd, and who subsequently threw off the Frankish yoke after the death of King Dagobert at the Battle of Castras. Arvor later placed itself under Visigothic and West Roman protection, but was always allowed much more freedom than it had had under the Franks.
In 1078 King Hywel Gorchfygwr ap Cynan invaded and conquered Prydain after a dynastic dispute concerning the succession to the throne of that kingdom. Arvor and Prydain remained in close contact for several centuries, and were later joined by Lyonesse after the royal house succeeded there as well. By the time King Gwilym IV ap Emrys died in 1413 Arvor had become a minor backwater in the greater Jersiais realm, and it was slowly absorbed and ultimately annexed into Lyonesse during the reigns of his successors.