The Ramlat al-Sab'atayn (Arabic: رملة السبعتين) is a region of desert in north-central Yemen. It comprises mainly transverse and seif dunes and covers an area of about 100 by 240 kilometres (60 by 150 mi), roughly 26,000 square kilometres (10,000 sq mi). The area includes part of what was known to medieval Arab geographers as the Ṣayhad. It extends from al-Khawr to the edge of the Rub' al-Khālī or Empty Quarter. It includes the Yemeni muhafazahs of al-Jawf, Ma'rib and Shabwa.