Rather than the enormous masonry that made the Egyptian pyramids, ziggurats were built of much smaller sun-baked bricks. Like the pyramids, ziggurats had mystical purposes as shrines, with the top of the ziggurat the most sacred spot. The legendary "Tower of Babel" was one such ziggurat. There was significance in the number of levels on the way to the top, and the placement and incline of the ramps.
The first ziggurat dates back some 3 millenniums B.C. The latest dates from around 600 B.C. There are fascinating parallels between the ziggurats of Mesopotamia and the temples of Maya culture in Central America.
Herodotus' Histories includes, in Book I (para. 181), one of the more famous descriptions of a ziggurat: "In the middle of the precinct there was a tower of solid masonry, a furlong in length and breadth, upon which was raised a second tower, and on that a third, and so on up to eight. The ascent to the top is on the outside, by a path which winds round all the towers. When one is about half-way up, one finds a resting-place and seats, where persons are wont to sit some time on their way to the summit. On the topmost tower there is a spacious temple, and inside the temple stands a couch of unusual size, richly adorned, with a golden table by its side. There is no statue of any kind set up in the place, nor is the chamber occupied of nights by any one hut a single native woman, who, as the Chaldeans, the priests of this god, affirm, is chosen for himself by the deity out of all the women of the land."