Soltaniyeh situated in the Zanjan Province of Iran, some 240 km to the north-west from Tehran, used to be the capital of Ilkhanid rulers of Persia in the 14th century. Its name translates as "the Imperial". In 2005, UNESCO listed Soltaniyeh as one of the World Heritage Sites.
The central magnet of Soltaniyeh's several ruins is the Mausoleum of Il-khan Öljeitü also known as Muhammad Khodabandeh traditionally known as the Dome of Soltaniyeh.
The structure, erected from 1302 to 1312 AD, has the oldest double-shell dome in the world. Its importance in the Muslim world may be compared to that of Brunelleschi's cupola for Christian architecture. The Dome of Soltaniyeh paved the way for more daring Iranian-style cupola constructions in Muslim world, such as the Mausoleum of Khoja Ahmed Yasavi and Taj Mahal. Much of exterior decoration has been lost, but the interior retains superb mosaics, faience, and murals. People have described the architecture of the building as “anticipating the Taj Mahal.”
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