The city is an offshoot of the ancient city of Ṭūs and owes its historical importance to the burial place and shrine of the caliph Hārūn ar-Rashīd (d. AD 809) and that of Alī ar-Riḍāʿ (d. 818), the eighth imam of the Twelver Shīʿīte sect of Islām. Although Meshed was severely damaged in a Mongol attack in 1220, the sacred buildings were partially spared, and traces of the earlier structures remain. Shāh Rokh, the son of the conqueror Timur (Tamerlane), did much to beautify Meshed, and his wife erected a mosque that is one of the finest architectural achievements of Iran. In the 16th and 17th centuries, Meshed was sacked by Turkmen and Uzbeks. It was restored by Abbās Iʿ (reigned 1588–1629), who encouraged the pilgrimage and beautified the city. Nāder Shāh (Nādir Shāh) (reigned 1736–47) made it his capital and made several additions to its buildings. After Nāder's death, Meshed became the capital of a small state controlled by his grandson. Pop. (2006) 2,427,316.