In the long interval between the fall of the last Sumerian dynasty c. 2000 bc and 747 bc there are two substantial gaps in chronology, each about two centuries long. The earlier gap is in the 2nd millennium, from approximately 1600–1400 bc, the later gap in the 1st millennium, from c. 943–747 bc. During these gaps the names of most of the kings are known, as well as the order, but usually not the length of their reigns.

A means of checking the reliability of the Babylonian king list is provided by the chronicles, annals, and other historical texts that show that a given Assyrian king was contemporaneous with a given Babylonian king. There are no fewer than 15 such synchronisms between 1350 and 1050 bc, and, when the Babylonian and Assyrian king lists are compared, they all fit in easily. Only one of them, however, provides a close approximate date in Babylonian chronology. This synchronism shows that the two-year reign of the Assyrian king Ashared-apil-Ekur (c. 1076–c. 1075 bc) is entirely comprised within the 13-year reign of the Babylonian king Marduk-shapik-zeri. The Assyrian’s dates are probably correct to within one year. Thus, if Marduk-shapik-zeri is dated so that equal proportions of his reign fall before and after that of Ashared-apil-Ekur, a date is obtained for the former that should not be in error more than six years. This synchronism constitutes a key to the structure of Babylonian chronology by providing the base date for all the reigns in the interval c. 1400–943 bc for which the Babylonian king list gives figures. All the dates thus obtained are subject to the six-year margin of error.

These synchronisms between Assyrian and Babylonian kings continue throughout the period that corresponds to the second gap in the Babylonian king list—from c. 943–747 bc. Since the Assyrian chronology in that period is firmly established, these synchronisms provide a useful framework for the structure of Babylonian chronology in that period.

The gap in the 2nd millennium bc, however, is not as easy to fill. The fact that the magnitude of the gap is uncertain constitutes the main problem in the chronology of the 2nd millennium bc and also affects the chronology of the preceding Sumerian period. The problem is not yet solved. Observations of the planet Venus made during the reign of King Ammisaduqa, less than 50 years before the end of the 1st dynasty of Babylon, permit only certain possible dates for his reign. Translated into dates for the end of the dynasty, the three most likely possibilities are 1651, 1595, and 1587 bc. The evidence is not yet conclusive and leaves uncertain what choice should be made among the three. The chronology adopted here is based on the second of these dates for the end of the 1st Babylonian dynasty—i.e., 1595 bc.

Prior to this gap in the 2nd millennium bc, there is a period of five centuries with a well-established chronological structure. All the kings in the major city-states are known, as well as their sequence and the length of their reigns. Which sets of dates should be assigned to these reigns, however, depends on the date adopted for the 1st dynasty of Babylon. This period of five centuries extends from the beginning of the 3rd dynasty of Ur to the end of the 1st dynasty of Babylon—i.e., on the chronology adopted here, 2113–1595 bc. During this period the Babylonians dated their history not by regnal years but by the names of the years. Each year had an individual name, usually from an important event that had taken place in the preceding year. The lists of these names, called year lists or date lists, constitute as reliable a source in Babylonian chronology as the eponym lists do in Assyrian chronology. One of the events which almost invariably gave a name to the following year was the accession of a new king. Hence, the first full regnal year of a king was called “the year (after) NN became king.” In Assyria the number of personal names in an eponym list between the names of two successive kings normally equalled the number of years in the reign of the first king, and, similarly, in Babylonia the number of year names between two year names of the above kind nearly always equalled the number of years in the reign of the first king. Just as in Assyria, the eponym lists are almost certainly the source of the king lists, so in Babylonia the king lists are based on the year lists. Several of these king lists, compiled at a time when the year lists were still in use, survive. One gives the 3rd dynasty of Ur and the dynasty of Isin; another gives the dynasty of Larsa. Both may be school texts.

The 3rd dynasty of Ur and the dynasty of Isin also figure in the Sumerian king list, which reaches far back into the Sumerian period. The original version probably ended before the 3rd dynasty of Ur, but later scribes brought it up to date by adding that dynasty as well as the dynasty of Isin.