Stepping back in time beyond the Eponym List relies primarily on the Assyrian King List. The AKL provides the basis for Mesopotamian history prior to 900 BC. It is preserved in two nearly complete copies, a damaged version, and several fragments.
Over one hundred Assyrian kings are recorded in the AKL. The earliest rulers have only their name and genealogy registered, but beginning c. 2000 BC the AKL specifies the number of years the kings reigned. The AKL timeline spans more than a thousand years, reaching to the ninth and eighth century BC where AKL overlaps the Eponym List. The two lists match. [See frame 7]
The possibility of determining the interval between dates in a local calendar rests on two premises: the existence of an "official" time scale that was not altered arbitrarily, and a means of linking a local calendar to the time scale.
In Assyria, the Eponym List served as a fixed time scale - one eponym, one year. Numerous vestiges of 2nd millennium BC year-names suggest that a comprehensive list once existed back to c. 2000 BC. Armed with this record, a scribe writing a kings list would have no trouble tallying regnal years. If he erred, the overall chronology would be unaffected, since the miscue would be reversed later on. In such a scheme, the list of year-names constituted a timeline and the accession years of the kings appeared as marks on the line.
The reliability of the AKL chronology does not rely solely on a hypothetical long list of eponyms. The documentation from Assyria is immense, and a great deal of evidence has been amassed in support of conventional chronology. Still, irregularities in the data continue to fuel energetic debate and unorthodox chronologies.
A particularly contentious debate swirls around interpretations of the Venus Tablets. Inscriptions on the tablets furnish the only collection of planetary observations dated earlier than the 7th century BC. The text gives an account of the comings and goings of Venus over a period of 21 years. The observations must have been considered significant, as more than ten independent sources of the text are preserved.
The inscriptions include the day and month of first and last visibility of Venus, and also the number of days the planet was invisible. A reference to the Year of the Golden Throne dates the tablets to the 8th year of Ammizaduga, a Babylonian king who lived long before the 1st millennium.
Chronologies based on these records claim an absolute timeline that reaches to the early 2nd millennium BC.
The abundance of astronomical information on the tablets should have made the dating of Ammizaduga straightforward and thus provide a key chronological marker - a rock-solid early absolute date.
Nevertheless, the Venus astronomy proved thorny. Historians have labored over the data for more than a century without arriving at a definitive date. The observations do not seem to make sense; they do not at all correspond to the current orbit of Venus. Consequently, contemporary analysis proceeds on the basis that the record is corrupted.
A statistician who dealt with the Venus text at length laments that he never contended with a worse data set. Consequently he screened out 18 records and analyzed the remaining 31 observations. His statistical calculations point to 1702 BC as the most probable date for Ammizaduga Year 1.
Recently, a new chronology fashioned in academe surfaced in the popular press. It settles on 1550 BC for Ammizaduga Year 1. However, the date and the chronology are not without critics.