Al-ʿAwāṣim (Arabic: العواصم‎, "the defences, fortifications"; sing. al-ʿāṣimah, اَلْـعَـاصِـمَـة, "protectress") was the Arabic term used to refer to the Muslim side of the frontier zone between the Byzantine Empire and the Umayyad and Abbasid Caliphates in Cilicia, northern Syria and Upper Mesopotamia. It was established in the early 8th century, once the first wave of the Muslim conquests ebbed, and lasted until the mid-10th century, when it was overrun by the Byzantine advance. It comprised the forward marches, comprising a chain of fortified strongholds, known as al-thughūr (اَلـثُّـغُـوْر; sing. al-thagr, اَلـثَّـغْـر, "cleft, opening"), and the rear or inner regions of the frontier zone, which was known as al-ʿawāṣim proper. On the Byzantine side, the Muslim marches were mirrored by