Ducellier 1999, p. 780: "As for Albania, its separate identity was real enough, even though it had not truly broken with Constantinople; all the same, the rulers of Arbanon around ἄρχον, Progon and his sons Dhimitër and Gjin, based at Kruja, retained a considerable degree of autonomy, even though Progon bore no title grander than ἄρχων (archon); and the title of πανὑπερσεβαστός (panhypersebastos), borne by Dhimitër at the start of the thirteenth century, can only be seen as a sign of his dependence on the Byzantines." Ducellier, Alain (1999). "24(b) – Eastern Europe: Albania, Serbia and Bulgaria". In Abulafia, David (ed.). The New Cambridge Medieval History: Volume 5, c.1198 – c.1300. Cambridge: Cambridge University Press. pp. 779–795. ISBN978-0-52-136289-4.
Clements 1992, p. 31: "By 1190, Byzantium's power had so receded that the archon Progon succeeded in establishing the first Albanian state of the Middle Ages, a principality." Clements, John (1992). Clements' Encyclopedia of World Governments. Vol. 10. Dallas, TX: Political Research, Incorporated.