The Evolution of the Sumerian Pantheon as Evidenced in its Writtings

There is a gradual diminution of the pantheon back through the stages represented by four periods of early writing before 3000 B.C. until at Erech only two deities are found. The Sumerian theologians themselves had two views about the oldest deity from which the whole vast pantheon sprang. The philosophically minded, basing their theory on the well-known Sumerian principle that the whole universe and all things in it were derived from the logos or word of the Water-God, regard the Water-God as the first deity. Another school which probably preserves the true tradition and true fact, always regards the Sky-God as primitive and founder of the pantheon.

Langdon, Stephen H., “Monotheism as the Predecessor of Polytheism  in Sumerian Religion” (pp. 136-46), Evangelical Quarterly, London: James Clarke & Company, vol. 9 (April) 1937, p. 138.