 The walls of Byllis carry more than four inscriptions with details regarding their construction by the engineer Victorinus, as ordered by Emperor Justinian I (483-565).One of the participants in the Council of Ephesus in 431 was a Felix who signed once as Bishop of Apollonia and Byllis, at another time as Bishop of Apollonia.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.