The exact etymology of the word Serb is obscure, but one theory is that
it comes from the Caucasian ser, meaning "man",
with a plural
suffix of bi from that language added. The name Serb was first
mentioned in the 6th century A.D. by geographer Vibius Sequestrus. The first Serbs
in Germany appeared at the beginning of the 6th century in the Magdeburg
and Anhalt regions. The German city of Zerbst (Serbis"te in Slavic)
is a remainder of the early invasion. Serbs in the
Balkan Penninsula are first mentioned
in 822 by Einhard, of Charlemagne's court, but the Byzanthine
emperor Constantine
VII Porphyrogenitus, writing in the 10th century, refers to Serbs as already
being in Illiric province by the middle of the 7th
century.
Serbs were one of the peoples of the Caucasus and lived on the Eastern
shores of Sea of Azov. At the time of the barbarian invasions, they began
to move with other Slavs toward the west, a progress that began as early
as the 4th century...According to the emperor Constantine Porphyrogenitus, the emperor Heraclius (610-640) Invited the serbs to settle in the devastated north-western provinces of the Byzantine empire and to defend them against the incursions of the avars.