A battle in northern Greece between a coalition of Franks, led by William II of Villehardouin, prince of Achaia, and a Byzantine army from the Empire of Nicaea.
In 1257, the forces of Manfred of Staufen, king of Sicily, occupied the port of Durazzo (mod. Durrës, Albania) and parts of Albania and Epiros as well as the island of Corfu (mod. Kerkira, Greece). In order to regain some of his losses, Michael II, despot of Epiros, married his daughter Helena to Manfred, and another daughter, Anna, to William II of Achaia. After the death of Theodore II Laskaris, emperor of Nicaea, Michael II planned to expand his territory toward Thessalonica (mod. Thessaloniki, Greece) with the support of his sons-in-law. During the spring of 1257, William joined his troops with these of Michael II, the latter’s illegitimate son John Doukas, and Manfred’s knights from Sicily. Meanwhile the emperor of Nicaea, Michael VIII Palaiologos, sent his brother John with a large army to Macedonia. When Michael II and John Doukas abandoned the alliance, the outnumbered Franks and Sicilians were heavily defeated at Pelagonia in Macedonia (summer 1250). Prince William and many barons were taken prisoner.
Pelagonia was a prelude to important alterations in the political landscape. On 25 July 1261 Constantinople was recaptured from the Latins, while Prince William and his barons were freed only after having agreed to deliver to the Byzantines several castles in the Peloponnese (end of 1261).