A battle fought on 15 March 1311, between Walter I, duke of Athens, supported by many of the leading knights of Frankish Greece, and the Catalan Company, the duke’s former mercenaries, whom he was trying to dismiss from his service and remove from his duchy.
The battle was decisive in that many members of the French ruling element in central Greece were slaughtered and replaced by the victorious Catalans. Like other battles of the fourteenth century, it demonstrated how well-drilled foot soldiers with crossbow support could trounce an army of mounted knights. The site of the battle is not securely known. The medieval writers RamônMuntaner and Nikephoros Gregoras both located the battle on the marshy plain of the Kephissos in the region of Orchomenos; in this they were followed by all writers before 1940, who thus named the engagement the battle of the Kephissos. In 1940 a hitherto unknown letter of Marino Sanudo came to light; written in 1327, it referred to the battle taking place near Halmyros, presumably at or near the modern town of Halmyros, just south of modern Volos on the Pagasaitic Gulf.