Battle of Halmyros
1311 CE.
Shown on the map at 39.159°, 22.840°.
The Battle of Halmyros, known by earlier scholars as the Battle of the Cephissus or Battle of Orchomenos, was fought on 15 March 1311, between the forces of the Frankish Duchy of Athens and its vassals under Walter of Brienne against the mercenaries of the Catalan Company, resulting in a decisive victory for the mercenaries. Engaged in conflict with their original employers, the Byzantine Empire, the Catalan Company had traversed the southern Balkans and arrived in southern Greece in 1309. The new Duke of Athens, Walter of Brienne, hired them to attack the Greek ruler of neighbouring Thessaly. Although the Catalans conquered much of the region for him, Walter refused to pay them and prepared to forcibly expel them from their gains. The two armies met at Halmyros in southern Thessaly (or at the Boeotic Cephissus, near Orchomenos, according to an earlier interpretation). On the Athenian side, many of the most important lords of Frankish Greece were present. The Catalans were considerably outnumbered and weakened by the reluctance of their Turkish auxiliaries to fight.
Text from the Wikipedia article Battle of Halmyros, licensed CC BY-SA 4.0.