Byllis is an ancient city located in Fier County, Albania. It was founded during the Hellenistic period in the 4th century BC on the territory of the Illyrian tribe of Bylliones. During the Roman rule, the city was a Roman colony called Colonia Bullidensis. Byllis walls bear several inscriptions indicating their construction according to the orders of the Byzantine Emperor Justinian I (483-565 AD).