Russia

Arthurian lore made this the realm of King Baraton.

In Layamon’s Brut, the daughter of Russia’s king marries King Alcus of Iceland, a vassal of Arthur.

Its kings in Claris et Laris are Solifas, who joins Emperor Thereus of Rome’s war against Arthur, and Baraton, who joins King Tallas of Denmark in a war against Urien.