City (pop., 2006: 1,398,060), northwestern Iran. Earthquakes have damaged the city numerous times, and it has weathered invasions by Arabs, Turks, and Mongols. The Turkic ruler Timur conquered it in 1392. During the next 200 years control passed several times between Safavid Iran and the Ottoman Empire. During the 19th and 20th centuries it passed between the Ottomans and the Russian Empire, and the same powers fought over it in World War I (1914–18). In the 1850s a schismatic Shi'ite religious leader known as the Bab (Gateway) and 40,000 of his followers were executed there. It was damaged during the Iran-Iraq War (1980–88). Notable ancient sites include the 15th-century Blue Mosque, renowned for the splendour of its blue tile decoration, and the remains of the 12-sided tomb of Mongol leader Mahmud Ghazan.