Byllis (Albanian: Bylis; Greek: Βύλλις; Latin: Byllis) or Bullis or Boullis (Βουλλίς) was an ancient city and the chief settlement of the Illyrian tribe of the Bylliones,^[1][2] traditionally located in southern Illyria. In Hellenistic times the city was either part of Illyria or Epirus. In Roman times it was included within Epirus Nova, in the province of Macedonia.^{[3][4][5][6][7][8]} The remains of Byllis are situated north-east of Vlorë, 25 kilometers from the sea in Hekal, Fier County, Albania. Byllis was designated as an archaeological park on 7 April 2003 by the government of Albania.^[9]

The massive walls of Byllis were built around 350 BC when the Illyrians went through a dynamic development founding their own cities. The urban settlement was built on the territory of the community of the Bylliones on an already existent Illyrian hilltop proto-urban area dating back to the previous century.^[10] Later Byllis acquired the trappings of a Hellenistic town,^[11] and because the southernmost Illyrian tribes, including the Bylliones, were inclined to become bilingual, it was also a Greek-speaking city.^[12] Byllis received sacred ancient Greek envoys, known as theoroi, during the early 2nd century BC, which only cities that were considered Greek were eligible to receive.^[13] The time duration that passed before Illyrian cities were documented on a list of theorodokoi clarifies that acculturation did take place in southern Illyria, however it indicates that the process was gradual.^[14]

During the Roman-Illyrian war in 169/168 BC the Bylliones took part on the Roman side against the Illyrian king Gentius. However, the subsequent alliance of Byllis with Molossians and Macedonians led to its sacking and destruction by the Romans. After a long decline, in 30 BC the city became a Roman colony. In Roman times Byllis rose again, also becoming a bishopric in late antiquity.^[15]