Wikipedia
Burtas (, Burtasy; , Părtassem; ) were a tribe of uncertain ethnolinguistic affiliation inhabiting the steppe region north of the Caspian Sea in medieval times (modern Penza Oblast, Ulyanovsk Oblast and Saratov Oblast of the Russian Federation). They were subject to the Khazars.
The ethnic identity of the Burtas is disputed, with several different theories ranging from them being a Uralic tribal confederacy (probably later assimilated to Turkic language), and therefore perhaps the ancestors of the modern Moksha people, or that they were an Iranic tribe, possibly the ancestors of the modern Mishars, and/or Volga Tatars and Chuvash.
Recently, some scholars have suggesting that the Burtas were actually Alans or another Iranian ethnolinguistic group. The Alanic ( Sarmatian) origin is also derived from their name Burt-as / Beehive-asses (Burt is Turkic for beehive) and Asses is Alanic selfname, as Ossetians (Caucasian Alans) and Jasses ( Jasz, Hungarian Alans) all used the same name.