Ziggurat is the name commonly given to the vaguely pyramid-shaped, stepped structures (ziqqarratu) built in many temple compounds in Mesopotamian cities from c. 2200 BCE until c. 550 BCE. Unlike Egyptian pyramids, ziggurats were of solid construction (mostly mud brick and bitumen), lacking internal chambers. The upper platforms of ziggurats supported one or more shrines, at least one generally sacred to the patron god of the city in which the ziggurat was located. Where indications have survived, they reveal that access to the upper platform was by either exterior triple stairway or by a spiral ramp. Ziggurats were generally rectangular structures, typically averaging 40 x 50 m at the base. No ziggurat has retained its original height.