"During the early Islamic conquests, the Muslims took possession of many cities in northern Syria as early as the mid-seventh century. When the Muslim-Arab armies advanced, the Byzantine emperor Heraclius evacuated the frontier defenses, which became known as [the frontier]... This front zone, a kind of no-man's land, was open to attacks from both sides and constituted the forward strongholds from which raids to Byzantine territories were undertaken." Isom-Vahaaren & Schull, 32