The Battle of Isaszeg was fought between King Béla IV of Hungary and his son, Stephen, who served as Junior King and Duke of Transylvania. Stephen defeated his father's army in the subsequent peace Béla was obliged to cede the government of the Eastern parts of his kingdom again to his son.
On 23 March 1266, father and son confirmed the peace in the Convent of the Blessed Virgin on the Nyulak szigete ('Rabbits' Island').
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Battle of Isaszeg (1265) Wikipedia(Text) CC BY-SA