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 in Soltaniyeh city, Zanjan Province. It is one of the UNESCO World Heritage Site.
The structure, erected from 1302 to 1312 AD, has the oldest double-shell dome in Iran. This erroneous view of the construction was made by Dieulafoy but is totally disputed by Andre Godard. In Godard's view it is a normal, if spectacularly large dome, with a thin skin on top for the faience and is in no way a double dome. Its importance in the Muslim world may be compared to that of Brunelleschi's cupola for Christian architecture. It is one of the largest brick domes in the world, just at the theoretical engineering limit for a brick dome and the third largest dome in the world after the domes of Florence Cathedral and Hagia Sophia.
The Dome of Soltaniyeh paved the way for more daring Iranian-style cupola constructions in the Muslim world, such as the Mausoleum of Khoja Ahmed Yasavi and the Taj Mahal. Much of its 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.”