The mosque was expanded during the Seljuq (1038-1118), Ilkhanid (1256–1335) and Timurid (1370–1507) eras. The mosque has a courtyard, a large Iwan (a vaulted hall, walled on three sides and open on one side), a western Maqsurah (an enclosure near the prayer niche or Mihrab), and three Shabistans (inner sanctum) in the north, south and east.
The 21-meter iwan has tiled inscriptions on three sides. The southern Shabistan has 27 rooms and 16 pillars. Built during the reign of Ilkhanid ruler Arghun Khan (1258-1291), this Shabistan was renovated during the reign of Fath-Ali Shah Qajar (1772–1834).
The mosque’s Seljuq era minaret stands over 20 meters tall and is located in the northeastern part of the structure. Brick Kufic inscriptions encircle nearly 2 meters of the length of this minaret. The Jame Mosque of Semnan is a National Heritage Site.
Source: To Iran