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About 100 km (62 mi) south-west of Qazvin are the tombs of two Saljuki era princes — Abu Saeed Bijar, son of Sa'd, and Abu Mansur Iltai, son of Takin — located in two separate towers known as the Kharraqan twin towers. Constructed in 1067 CE, these were the first monuments in Islamic architecture to include a non-conic two-layered dome. Both towers were severely damaged by a devastating earthquake in March 2003.