The exact time of construction is not known with certainty. Some historians believe the founder is Shapour I who ruled Persia from 242 to 272 AD and some other believe that construction possibly began during the reign of Anushiruwan the Just (Khosrow I) after a campaign against the Byzantines in 540 AD. The arched iwan hall, open on the facade side, was about 37 meters high 26 meters across and 50 meters long, the largest man-made, free standing vault constructed until modern times.