Dating Hammurabi, the sixth king of Babylon

The Greek geometer Pythagoras, whose theorem is familiar to every student of mathematics, lived about 500 BC but the theorem was known to the Babylonians much earlier.

The Babylonians used a numbering system based on 60. We find a residue of this in our own measurement of time and of angles. They also invented the place value system, where a numerical symbol has different meanings in different positions.

We know of the ancient Middle East mainly through a vast collection of clay tablets with cuneiform inscriptions. Cuneiform is one of the earliest writing systems, with wedge-shaped marks made by a stylus in the soft clay, which is then baked dry. Laws, letters, accounts, stories and mathematics were all impressed on clay tablets.

Irish clergyman Edward Hincks, a fellow of Trinity College and member of the Royal Irish Academy, carried out one of the earliest decipherments of cuneiform. He studied a tablet now in the British Museum, and determined that it listed specific dates on which Venus appeared as a morning or evening star. The dates were in the Assyrian lunar calendar and their precise interpretation was uncertain.

The Reign of Hammurabi

The Code of Hammurabi is among the first written legal systems in history. Hammurabi, the sixth king of Babylon, flourished in the 18th century before Christ, but the exact dates of his reign are uncertain: estimates extend over more than two centuries.

In a recent discourse at the Royal Irish Academy, Prof Werner Nahm revisited some century-old scholarship and found that the date when Hammurabi first reigned could be fixed, by known astronomical events, to one of four years. Nahm, director of the school of theoretical physics of the Dublin Institute for Advanced Studies, is also expert in reading and interpreting ancient cuneiform script.

Nahm examined digitally enhanced images of a newly found tablet now in Ankara and was able to establish the first year of Ammizaduqa, the great-great-grandson of Hammurabi. A reference to a solar eclipse in the Assyrian year 127, when Puzur-Ishtar was governor, enabled him to establish the dates for Hammurabi precisely. There were 195 years between the solar eclipse and the first year of Ammizaduqa. Genealogical records then showed the beginning of Hammurabi’s reign to be 1784 BC.

Pinning down dates like this is important. Potentially grave consequences of the changing climate loom before us. Such changes, both short and long-term, have occurred before. The Mesopotamian civilisation declined after Hammurabi, and many cities were abandoned. Babylon itself lay in ruin for some time. While military decline was one factor, there were others. The simultaneous collapse of the Egyptian civilisation, a thousand miles away, lends support to a major perturbation of the climate.

The inscription on one tablet describes a period when Venus, which should have been prominent, was unobserved. This may well have been due to the obscuring effect of volcanic dust. Volcanic events are known to cause crop failure and famine for a year or more.

Evidence of a climate downturn about the year 1627 BC is found in the tree rings of Irish bog oak, analysed by Mike Baillie of Queen’s University Belfast. A possible link to the eruption of Santorini, which wiped out the Minoan Empire in Crete, is intriguing but, to date, unproven.

Peter Lynch is professor of meteorology at University College Dublin. He blogs at thatsmaths.com