Battle of the Cephissus The Battle of the Cephissus , also known as the Battle of Halmyros or Orchomenos , was fought on 15 March 1311 between the Frankish Greek forces of Walter V of Brienne and the mercenaries of the Catalan Company , resulting in a devastating victory for the Catalans . Background . Walter V had hired the Company to defend his Duchy of Athens from the neighboring Greek states the Despotate of Epirus , the Byzantine Empire , and the Vlach - inhabited entity called Great Wallachia . This they did with great success , but Walter attempted to discharge them , picking a moiety of the company and paying them lavishly to remain in his service , while ordering the expulsion of the rest without their pay . When the Company resisted , Walter assembled the feudal host of Frankish Greece , with reinforcements sent from Naples , assembling 700 Frankish knights and native Greek horsemen , a large number of infantry , mostly native Greeks ( set at 24 , 000 by Muntaner ) , as well as the 200 horsemen and 300 footmen he had selected from the Catalan Company . Battle . The Company assumed a defensive position on the plain of Orchomenus , near the River Cephissus . Their Turkish auxiliaries took up a separate position nearby , thinking the quarrel was a pretext arranged by the Company and the Duke of Athens to exterminate them . To protect their position , the Catalans broke dikes and dug trenches , diverting water from the Cephissus to flood the fields lying in front of them . On the eve of battle , the Catalans in the Duke ' s service , stricken by conscience , took leave of him and rejoined the Company . This circumstance little disturbed the Duke , who still outnumbered the company , and had at his command the chivalry of the Frankish states in Greece , considered the flower of the French - speaking world . The Duke , with his banner in the vanguard , opened the battle with a cavalry charge against the Catalans , followed by the infantry . In the morass covering the Catalan front , the cavalry soon became hopelessly mired , the Duke and his banner falling in a rain of javelin s from the almogàvers . As the lightly equipped Catalans advanced to cut down the wallowing knights , the Turkish auxiliaries descended from their camp upon the Athenian army , panicking and routing what remained of it . According to Muntaner , only two of the seven hundred knights survived the battle , Roger Deslaur and Boniface of Verona . However , Nicholas Sanudo , later Duke of the Archipelago , also escaped , and a few others , like Antoine le Flamenc , were probably ransomed . Muntaner claims that 20 , 000 of the infantry were killed , and all of the native horse . Aftermath . The battle is sometimes compared to the Battle of Agincourt where light , missile - armed troops were able to defeat heavily encumbered opponents hindered by adverse terrain . The paralyzing charge into the bogs and the slaughter that followed resulted in the near annihilation of the nobility of the Principality of Achaea and its vassal states . The Catalan Company proceeded to occupy the Duchy of Athens , which they placed under the protection of a prince of the House of Aragon and ruled until 1379 . This tremendous smash also ended the golden age of Frankish chivalry in the Duchy of Athens . The remaining Latin states would now be largely dependent on external powers such as Naples and Venice for support .