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.

[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.

[25] Byllis was founded on the territory of the Illyrian community of the Bylliones around 350 BC, on an already existent proto-urban area dating back to the previous century.

[15] In the sanctuary of Dodona a 4th-century BC inscription on a lead foil provides the earliest known attestation of the Bylliones, asking to which deity they should sacrifice in order to ensure the safety of their possessions.

[30] The city experienced a notable development in the Hellenistic period, representing the chief settlement of the Illyrian koinon of the Bylliones,[31] of which several hilltop centers are found in the lower valley of the Aoos river.

[16] The creation of Hellenistic cities such as Byllis in the territory of southern Albania has been attributed to the successors of Alexander the Great and Pyrrhus of Epirus.

[36] Archaeological explorations have not yet found a sanctuary or temple in the city of Byllis, however, a series of inscriptions show the adoption of the Ancient Greek cults of Zeus, Hera, Dionysius and Artemis.

[41] In the 21st century scholars consider Byllis as an Illyrian city that later acquired the trappings of a Hellenistic town, becoming very much organized on a Greek model.

[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] In the Hellenistic era (3rd century BC) a stadium, a theatre, an agora, two stoas, a cistern and a peristyle temple were built in the city.

[citation needed] In 2011 during a road reconstruction near the archaeological park found in the site a statue of the Hellenistic era, which may depict an Illyrian soldier or a war deity, was discovered.

[51] After a long decline, the city rose again in 30 BC as a Roman colony,[15] which is attested by epigraphic material and by Pliny the Elder,[15] who called it Colonia Bullidensis.

[53] The walls of Byllis carry more than four inscriptions written in Greek with details regarding their construction by the engineer Victorinus, as ordered by Emperor Justinian I (483-565).

Some assume that the two towns formed a single episcopal see, others suppose he was, strictly speaking, Bishop only of Apollonia, but was temporarily in charge also of Byllis during a vacancy of that see.