In 264/878, Ahmad ibn Tulun was encouraged to occupy Syria and used the contexts of engaging in holy war against the Byzantines along the Thughur (the frontier between Muslim Syria and Byzantine Anatolia). Such a justification harkens back to the revolt of 249/863 against al-Mu`stain after a defeat at the hands of the Byzantines convinced the military that the caliph could not protect the lands of Islam. This campaign was cut short when `Abbas, the son of Ahmad ibn Tulun and his regent in Egypt, attempted to revolt. As a result of this revolt, Khumarawayh was declared successor to Ahmad ibn Tulun.