And to walk down “historical movie road” the Sarmatian cavalry played a major part in the movie “King Arthur” that stared Clive Owen as Arturius, a Roman cavalry commander.
Lancelot: [voiceover] By 300 AD, the Roman Empire extended from Arabia to Britain. But they wanted more. More land. More peoples loyal and subservient to Rome. But no people so important as the powerful Sarmatians to the east. Thousands died on that field. And when the smoke cleared on the fourth day, the only Sarmatian soldiers left alive were members of the decimated but legendary cavalry. The Romans, impressed by their bravery and horsemanship, spared their lives. In exchange, these ...
See: https://www.imdb.com/title/tt0349683/?ref_=nv_sr_2
:^) Yeah, I'd seen that view (Artorius as Arthur) presented as history, as well. There was some sort of post-Roman Romano-British successor state -- it built the Wansdyke across its southern boundary, had control of the Cornish peninsula (indeed, probably persiisted there the longest; it wasn't added to the Anglo-Saxon realms until Aethelstan), built so-called Offa's Dyke (the RC dating of the facing, much smaller barrier, Wat's Dyke, came back centuries older than Offa, and finally someone took the time to get a real dating for Offa's Dyke, it was also centuries older), relied on Hadrian's Wall for its northern boundary, and possibly relied on the density of population and cavalry for their eastern boundaries. The Car Dyke, a 2nd c Roman canal, remains in use today, and probably indicates a Roman-era population shift to the midlands.