There have been many different suggestions concerning the function of a ziggurat, and the issue is far from settled. Brevard S. Childs presents a brief summary of some of the major opinions:
The older view that the ziggurat was a representation of a mountain, brought from the mountainous homeland of the Sumerians to Babylon, has been shown as only a secondary motif by recent investigation. Busink has demonstrated from Eridu that the original ziggurat had nothing to do with a mountain. However, in that the Babylonians later on compared the ziggurat to a mountain, this may well be at the best a secondary motif acquired during its later development. Then again, Dombart's attempt to find in the ziggurat a throne concept has found little acceptance. Andrae advanced in 1928 the view that the temple-tower must be seen as a unity, the former being the dwelling place of the god, the latter his place of appearing.One of the earliest interpretations understood the ziggurat as the tomb of a king or a god (Hilprecht 1903: 469), although this was not necessarily considered the sole function. There were two major supporting arguments for this view. The first was the obvious similarity in shape to the early Egyptian pyramids. The second is connection in the inscriptional literature between the term ziggurat and gigunu, which was rendered "tomb" by Hilprecht (1903:462).
In regard to the former, the earliest pyramid, the so-called step-pyramid of Djoser at Saqqara, bears the closest resemblance to the ziggurat form. It has been demonstrated that the architectural form of the Egyptian pyramids began as a simple mastaba and was built up in several stages (Edwards 1946: 46ff). The step-pyramid was a product of the third dynasty in Egypt (mid-third millennium BC), which was contemporaneous with the Early Dynastic period in Mesopotamia. Although the extant evidence seems to indicate that the architectural form of the ziggurat became fully developed by that period, the development had begun perhaps a millennium earlier. Thus the ziggurat form can in no way be seen as dependent on the pyramids. Furthermore, no literary or artifactual evidence has produced any indication that the ziggurat functioned as a tomb.
With regard to the latter argument, the gigunu is no longer understood as a tomb, but rather as a sanctuary at the top of the ziggurat (CAD G: 67-70), though the precise meaning of the word remains uncertain.
One approach to examining the function of a ziggurat -- and in my opinion, the only approach that can give objective data, given our present state of knowledge -- is to analyze the names given to the ziggurats in the various cities where they were built. Rather than attempting to use our own standard to judge what is a ziggurat and what is not, we will use a list of designated ziggurats from a Neo-Babylonian bilingual geographical list of 23 entries (Rawlinson 1861: 50: 1-23 a, b). Following is my translation of the list:
The other four may indicate a cosmological function, that is, they may indicate that the ziggurat symbolized the connecting link between heaven and earth, or between heaven and the netherworld. The ziggurat at Sippar, temple of the stairway (simmiltu) to pure heaven, is particularly indicative of such a function because of the occurrence of the simmiltu in the myth of Nergal and Ereshkigal (Gurney 1960: 123:13-14; 125:42-43).
In this tale, the stairway is used by Namtar, the messenger of Ereshkigal, to journey from the netherworld to the gate of the gods Anu, Enlil, and Ea.<9> It serves as the link between the netherworld and heaven.<10> That the simmiltu occurs in the name of one ziggurat and that another means the "Temple which links heaven and earth" (18) may indicate that the ziggurat was intended to supply a connection between heaven and earth--not for mortal use, but for divine use. This is supported to some degree by the total absence of the ziggurats in the cultic rituals. S. Pallis remarks...
Anyone who has perused the whole of the material is struck by the remarkable fact that Etemenanki [the fabulous ziggurat of Babylon] is nowhere mentioned in the description of the course of the [akitu] festival though numerous other sacred localities in Babylon are referred to. Nor do we meet with any reference to ceremonies performed here. Indeed, I believe I may add that beyond the constant reference to the building of Etemenanki or "its head" in the inscriptions of the Neo-Babylonian kings, and the frequent mention of it in hymns where it is referred to or invoked in conjunction with Esagila, Ekur and other temples, we find nothing about Etemenanki or its religious uses in the entire Assyro-Babylonian literature (1926: 103-104).<11>It cannot, of course, be concluded that the ziggurat was not used in the rituals. We can only say that whatever its use may have been, if it had one, it is unknown to us. While Pallis is addressing the situation with regard to the ziggurat of Babylon, we would add that the same is true of all of the ziggurats known from the ancient Near East. If the known literature were our only guide, we would have to conclude that people did not use the ziggurat for any purpose.<12>
The mountain terminology used in some of the names is also of interest. In ancient mythologies certain mountains were often considered to be the place where deity descended or dwelt. The Bible likewise implies such a connection. YHWH comes down on a mountain (Sinai, Ex. 19) and sacrifice is made on a mountain (Moriah, Gen 22; Carmel, 1 Kings 18). Moses, Aaron, and Elijah, three of the most central figures in Israelite religion, all go up into a mountain for the meeting with YHWH at the end of their lives. In the Ugaritic Baal-Anat cycle, the temple of Baal is built on the summit of Mount Zaphon. The motif is likewise present in Greek mythology, Mount Olympus being the home of the gods.
Although the function of the ziggurat cannot be identified with certainty, our study of the names, the use of the simmiltu in mythology, the use of mountain terminology, and the lack of reference to a function in the cultic practice of the people, leads us to put forth tentatively, as a working hypothesis, the following suggested function:
The ziggurat was a structure that was built to support the stairway simmiltu), which was believed to be used by the gods to travel from one realm to the other. It was solely for the convenience of the gods and was maintained in order to provide the deity with the amenities that would refresh him along the way (food, a place to lie and rest, etc.). The stairway led at the top to the gate of the gods, the entrance to the divine abode.Before we move on to consider the implications of this function of the ziggurat for the narrative of Genesis 11, we need to look at a few more elements that can be further explained in light of the narrative's Mesopotamian background.