This is one of the oldest mosques still standing in Iran, and it was built in the four-iwan architectural style, placing four gates face to face. An iwan is a vaulted open room. Theqibla iwan on the southern side of the mosque was vaulted with muqarnas during the thirteen hundreds. Muqarnas are niche-like cells. The mosque is the result of continual construction, reconstruction, additions and renovations on the site from around 771 to the end of the 20th century.