Severians

The Severians or Severyans or Siverians (Russian: Северяне; Ukrainian: Сiверяни; Belarusian: Севяране) were a tribe or tribal union of early East Slavs occupying areas to the east of the middle Dnieper river, and Danube. They are mentioned by the Bavarian Geographer (9th century), Emperor Constantine VII (956-959), by Khazars ruler Joseph (c. 955), and in the Primary Chronicle (1113).

The etymology of the name of Severians is uncertain. One theory propose derivation from the Slavic word for "north" (sěver; men of the north), but the Severians never were the northernmost tribe of Slavs. Another theory proposes Iranian derivation from the name of the Sarmatian tribe Seuer, with seu meaning "black". Some scholars argued that the Yehudah called Sawarta from the Kievian Letter (c. 930), written in Hebrew as SWRTH (read either as Sur'ata or Sever'ata), which is derived from Slavic sirota (orphan; in the letter sense possibly convert) or Magyar Savarti (black), can be connected to the Severians.

In the work by Bavarian Geographer the ethnonym is connected by the scholars to the Zeriuani, or Sebbirozi (by some scholars considered as the Sabirs).

It is considered that the Severians continued the East Slavic tribal union after the political disappearance of the Antae, and Dulebes, along the middle Dnieper valley, independent or under the Khazar policy. It is presumed they inhabited along the lower Desna and upper Sejm and Sula. Their main center is considered to be in Chernihiv ("black city"). However, as the Severians in the historical sources inhabited both Dnieper and one part Danube valley, and it's said that the Zeriuani realm was so great from it all Slavs traced their origin, Henryk Łowmiański considered that the Ruthenian Severians were Slavic mother-tribe.

...
Wikipedia