Leaving aside the primitive phases of the religion as lying beyond the ken of historical investigation, we may note the sharp distinction to be made between the pre-Khammurabic age and the post-Khammurabic age.
We thus find in the post-Khammurabic period the pantheon assuming distinct shapes.
We thus obtain four periods in the development of the Babylonian-Assyrian religion: (i) the oldest period from_ C. 3500 B.C. to the time of Khammurabi (c. 2250 B.C.); (2) the post-Khammurabic period in Babylonia; (3) the Assyrian period (c. 2000 B.C.) to the destruction of Nineveh in 606 B.C.; (4) the neo-Babylonian period beginning with Nabopolassar (625-604 B.C.), the first independent ruler under whom Babylonia inaugurates a new though short-lived era of power and prosperity, which ends with Cyrus's conquest of Babylon and Babylonia in 539 B.C., though since the religion proceeds on its undisturbed course for several centuries after the end of the political independence, we might legitimately carry this period to the Greek conquest of the Euphrates valley (331 B.C.), when new influences began to make themselves felt which gradually led to the extinction of the old cults.
This process, which reached its culmination in the post-Khammurabic period, led to identifying the planet Jupiter with Marduk, Venus with Ishtar, Mars with Nergal, Mercury with Nebo, and Saturn with Ninib.