sentences:  Many narrow valleys ("wadis") run along its sides, such as Wadi Hanifa, and a group of towns lie on its central section, including the Saudi capital, Riyadh.Many settlements have historically existed on either side of it as well, such as those of Sudair and Al-Washm.The Tweig escarpment is mentioned in Yaqut's 13th century geographical encyclopedia under the name "Al-'Aridh", though for the past few centuries that name has applied only to the central section of it, around Riyadh.