In 1303, Ghazan sent another letter to Edward I via Buscarello de Ghizolfi, reiterating his great-grandfather Hulagu Khan's promise that the Mongols would give Jerusalem to the Franks in exchange for help against the Mamluks. The Mongols, along with their Armenian vassals, had mustered a force of about 80,000 to repel the raiders of the Chagatai Khanate, which was under the leadership of Qutlugh Khwaja. After their success there, they advanced again towards Syria. However, Ghazan's forces were utterly defeated by the Mamluks just south of Damascus at the decisive Battle of Marj al-Saffar in April 1303. It was to be the last major Mongol invasion of Syria.