On the 3rd cent. BC Arsinoe II Queen of Egypt dedicated to the Sanctuary of the Great Gods the Rotunda, the largest closed circular structure of ancient times. The roof was covered with horseshoe-shaped tiles. Their size gradually decreased from the periphery to the center. The operation of the building remains enigmatic. Perhaps it hosted the thronosis, a ritual that took place in the first degree of initiation into the Mysteries of the Great Gods. Read more.