In the Vulgate Estoire del Saint Graal, Persia is ruled by King Label in Joseph of Arimathea’s time. Wolfram says that magic was invented in the city of Persida in Persia, and that Perceval’s father Gahmuret had adventures in the region.
De Ortu Waluuanii describes a war between Persia and the Roman empire over the city of Jerusalem, in which a young Gawain, in the service of the Roman Emperor, defeated a Persian champion named Gormundus and settled the dispute.
The daughter of the King of Persia appears at a Sparrowhawk Tournament in Wirnt von Grafenberg’s Wigalois. In the Alliterative Morte Arthure and Malory’s Le Morte Darthur, the area seems to be under the command of the Roman Emperor, Lucius; Persian warriors joined Lucius’s campaign against Arthur.