In late March 1265 Sultan Baibars, Muslim ruler of the Mamluks, laid siege to Arsuf. It was defended by 270 Knights Hospitallers. At the end of April the town surrendered. However, the Knights remained in their formidable citadel. Baibers convinced the Knights to surrender by agreeing to let them go free. Baibers reneged on this promise immediately, taking the knights into slavery.
References
Fall of Arsuf Wikipedia(Text) CC BY-SA