The name derives from the Aromanians or Vlachs, a chiefly transhumant ethnic group that has lived in several mountainous areas of the Balkans, descended from ancient Romance-speaking populations displaced by the Barbarian Invasions of Late Antiquity.
The Vlachs of Thessaly first appear in Byzantine sources in the 11th century, in the Strategikon of Kekaumenos and Anna Komnene's Alexiad). In the 12th century, the Jewish traveller Benjamin of Tudela records the existence of the district of "Vlachia" near Halmyros in eastern Thessaly, while the Byzantine historian Niketas Choniates places "Great Vlachia" near Meteora. The term is also used by the 13th-century scholar George Pachymeres, and it appears as a distinct administrative unit in 1276, when the pinkernes Raoul Komnenos was its governor (kephale). Thessalian Vlachia was apparently also known as "Vlachia in Hellas".
Medieval sources of the period also speak of an "Upper Vlachia" in Epirus, and a "Little Vlachia" in Aetolia-Acarnania, but "Great Vlachia" is no longer mentioned after the late 13th century, and disappears until the 15th century, when it was applied to Wallachia proper, north of the Danube.
- Koukoudis, Asterios - Great Wallachia and the Byzantine commonwealth (Η Μεγάλη Βλαχία κι η βυζαντινή κοινοπολιτεία) (Greek)
- Kazhdan, Alexander (1991). "Vlachs". In Kazhdan, Alexander. The Oxford Dictionary of Byzantium. Oxford and New York: Oxford University Press. pp. 2183–2184. ISBN 978-0-19-504652-6.
- Kazhdan, Alexander (1991). "Vlachia". In Kazhdan, Alexander. The Oxford Dictionary of Byzantium. Oxford and New York: Oxford University Press. p. 2183. ISBN 978-0-19-504652-6.