Ancient History Ping.
The Sarmatians were distant kin of the much earlier Scythians. After a period of contention with the Roman Empire, they were defeated and their highly effective cavalry were press-ganged into service as auxiliaries to the Roman army -- but in far-flung areas, out of contact with the rest of their people, who were resettled in places. The Sarmatian cavalry saw most of its service in Britain, and some attribute the practice of the medieval jousts to the Sarmatian roots (I doubt this, btw). Ethnically and linguistically, they effectively ceased to exist by the time the Empire fell apart in the west. Another related people were the Alans.