The Bylliones were an Illyrian tribe that lived near the Adriatic coast of southern Illyria, on the lower valley of the Vjosa river, in the hinterland of Apollonia. The Bylliones were firstly attested in epigraphic material from the oracle of Dodona dating back to the 4th century BC, and their koinon was firstly attested in a 3rd-century BC inscription from the same oracle. Their territory was trapezoidal on the right side of the rivers Luftinje and Vjosa, extending in the west to the Mallakastra mountains. The chief city of their koinon was Byllis. Another important centre of their koinon was Klos, an earlier Illyrian settlement later called Nikaia, as an inscription attests. The Bylliones also inhabited in the area of an ancient sanctuary of the eternal fire called Nymphaion.