Lundein
One of the ancient names of London and one from which the modern name may be seen to be directly derived. Its origin is slightly confused. Some say that it comes from the Old English Lud-Dun, a name given to the capital after Lud, mythical King of Britain, had fortified the walls, Lud-Dun meaning 'Lud's fortress'.
Others, however, say that it comes from Caer Lludd, a name of obviously Welsh origin, and that it was this name that degenerated into Caer Llundein, the 'Caer' later being dropped and the spelling slightly altered, both changes being made to eliminate the Welsh influence.
London Cathedral | The Legend of King Arthur