The new King Arthur movie claims to be based on a fresh “historical” take on the mythic king (which includes Guinevere in a leather bikini). Specifically, it references the speculation about a connection between the historical general that supposedly was the basis for the legendary figure of Arthur, and the Sarmatians, an Iranian people of nomadic horsemen who were recruited by the Romans (like many other barbarians) to serve in their military, and who were apparently stationed in roman Britain.
This article details the links between the Sarmatians and Arthurian Legend, which include the dragon banner (the source of “Uthur Pendragon”?) and the legends of the magic sword and the holy cup:
After hard but victorious battles, 5,500 Sarmatian/Alanian heavy cavalry (called cataphractarii, i.e. clothed fully in scale armour) consisting of prisoners taken in war were posted to Britain in 175.
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The closed society of Sarmatian cataphractarii in Britain was able to maintain its ethnic features during the Late Roman period and afterwards. One reason is that their troops, called cuneus Sarmatorum, equitum Sarmatorum Bremetennacensium Gordianorum were not part of any military organization in active service. Consequently, after the withdrawal of the Roman army, they continued to live on their accustomed sites (Chester, Ribchester, etc.). They were still called Sarmatians after 250 years. A semihistoric Arthur lived about A.D. 500. He was very probably a descendant of those Alan horsemen, a battle leader of the Romanized Celts and Britons against the Anglo-Saxons, who invaded Britain after the Roman army had withdrawn. Arthur and his military leaders could therefore manage to train the natives as armoured horseman after Iranian patterns against the attacks of Angles and Saxons fighting on feet until their victory at Badon Hill.
There’s more stuff here, including parallels between the sword in the stone and Sarmatian rituals, and the close parallels in the legend about a king’s retainers reluctantly obeying his dying command to throw his sword in a lake.
Naturally, the Sarmatian Arthur has annoyed some people, but apparently not many.