Wikipedia
The al-ʿAwāṣim (, "defences, fortifications"; sing. al-ʿāṣimah, "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 the al-thughūr (; sing. , al-thagr, "cleft, opening"), and the rear or inner regions of the frontier zone, which was known as the al-ʿawāṣim proper. On the Byzantine side, the Muslim marches were mirrored by the institution of the kleisourai districts and the akritai border guards.
The term thughūr was also used in the marches of al-Andalus and Mawara al-Nahr, and survived in historical parlance, to be revived by the Egyptian Mamluks in the 14th century, when the areas traditionally comprising the 'ʿawāṣim and thughūr in northern Syria and the northern Euphrates region came under their control.