By the 8th century, Slavs had occupied most of the Balkans from Austria to the Peloponnese, and from the Adriatic to the Black seas, with the exception of the coastal areas and certain mountainous regions of the Greek peninsula [REF].
Following the siege of Constantinople and the dissolution of the Byzantine Empire by the Fourth Crusade in April 1204, Thessaly passed to Boniface of Montferrat's Kingdom of Thessalonica in the wider context of the Frankokratia.