And why is it so hard to know?

Hammurabi was the king of Babylon. He reigned about 3800 years ago in Mesopotamia, in what’s now Iraq. You may have heard of his code of laws.

I say “about” 3800 years ago because there are several possibilities for exactly when he reigned. Right now, the leading hypothesis is 1792-1750 BCE, but it could also be 1848-1806 BCE, or 1728-1686 BCE. Or even 1696-1654 BCE.¹ Only the last two of these ranges overlap, and even then just barely. If we’re uncertain, why are those dates so specific?

The short answer is that we lost the relevant records, probably when civilization collapsed after the Sea Peoples invaded. Every date we know from before then relies on a single unearthed tablet recounting the motions of Venus.

1. Making history

Think about how we know when any event in history happened. Ideally, someone who was alive during or shortly after the event wrote down the date, and we have that piece of writing today. For most of history, that’s not quite enough info. Our current calendar era (known usually as AD “Anno Domini”, and sometimes as CE “Common Era”) was introduced in Late Antiquity, in a table for the date of Easter by Dionysius Exiguus from 525 CE.² So past 1500 years ago, we have to translate the date into our modern calendar.

That’s not too hard if we understand the calendar system. Historians from Ancient Rome referred to years since the founding of the city of Rome (“Ab Urbe Condita”), though those dates weren’t used in everyday life. We know they counted from the year we now call 753 BCE, so we can pretty easily match up AUC dates with AD/CE ones.

Another issue crops up once you get to at most about 2000 years ago: the years don’t have numbers. Or at least, not numbers from a consistent epoch. They might be numbered by regnal years into the reign of the current monarch or elected leader. This is still used officially in Japan, so 2025 is “Reiwa(令和) 7”, the 7^th year of the reign of emperor Naruhito.

Among the ancient Greek city states, who had no common ruler, historians would use the current Olympiad. These might be numbered, or named after who won the ancient Olympics’ most prestigious foot race, the stadion (about 200 yards). 2025 would be “the 2^nd year of the 33^rd modern Olympiad, in which Letsile Tebogo of Botswana won the 200 meter dash”.

For these sorts of dates, we need to rely on lists of kings or consuls or Olympic champions or whoever. Luckily for archaeologists of the Ancient Near East, these civilizations wrote in cuneiform on clay tablets. If a building full of scrolls catches fire, the scrolls burn away. If a building full of clay tablets catches fire, the tablets become pottery, which survives even better. So, we do have a decent number of documents available.

In Assyria, just north of Babylon, we have three copies of the king list that agree back to Assyrian king Aššur-dan I in 1178 BCE. We’ve also found a tablet matching up the reigns of Babylonian kings with their Assyrian contemporaries. Letters from Mesopotamian kings to Egyptian pharaohs also help us get context. But we can’t take this list all the way back to Hammurabi, because civilization collapsed.

2. The end of the world

The Late Bronze Age collapse started around 1200 BCE. Basically every organized society in the Eastern Mediterranean crumbled, or at least was severely weakened. This was the one with the invasion of the Sea Peoples, who came down the Mediterranean coast raiding everyone’s cities, before finally being defeated in an ambush by Ramses III of Egypt.

Scholars today think the Sea Peoples may not have been the root of the destruction, but a symptom of a deeper problem. One hypothesis is that the Sea Peoples were fleeing drought and environmental changes in the whole region, and attacked the already weakened civilizations out of desperation. And not every civilization in the area suffered equal destruction:³ Cyprus was relatively unscathed, while the nearby Hittite Empire in Anatolia disappeared from history entirely.

This definitely deserves its own post, or perhaps its own book (I recommend Eric H. Cline’s 1177 B.C.: The Year Civilization Collapsed). The relevant gap in the Babylonian king list is a couple centuries before the Late Bronze Age Collapse. But the collapse is plausibly when the records were lost, since so few people still knew how to read and write.

Before the gap, we have another list of kings, which includes Hammurabi. The challenge, then, is to find one date, any date, that we can use to match up this king list and our modern calendar: an “absolute chronology”.

3. The morning star and the wisdom of the trees

The Babylonians were really into astrology. They treated it almost like a science, or at least proto-science. This also deserves its own post. What’s relevant to chronology, though, is that the Babylonians kept detailed records of when Venus rose relative to the Sun and the Moon. We’ve found loads of copies (like 20) of one specific data table from the reign of Ammisaduqa, the 4^th ruler after Hammurabi. We know how all three of these celestial objects move through the sky, so we can use this table to identify candidate dates for Ammisaduqa’s reign, and from there dates for Hammurabi and the rest of the kings.

The Venus tablet of Ammisaduqa

We can back these dates up with eclipses, which the Babylonians also tracked as astrological omens. A total solar eclipse passes over each specific spot on Earth about once every 300 years on average, and they’re also predictable thousands of years into the past and future. But Mesopotamia was a big place, and they were good enough at watching the sky to notice partial and annular solar eclipses as well. So, there are a few possible matches between eclipses, the Venus tablet, and our astronomical calculations:⁴

Chronology name:   Ultra-low  Low       Middle    High
Hammurabi’s reign: 1696-1654  1728-1686 1792-1750 1848-1806

The Middle chronology is the older, established chronology, while the Ultra-low chronology is the upstart challenger (from 1998). The Ultra-low chronology fits the eclipses better and arguably meshes better with the texts we’ve uncovered. On the other hand, it’s a bad fit for the radiocarbon dating we’ve been able to do.

Another independent point of evidence for the Middle chronology comes from dating tree rings in unearthed wood. At Kanesh, an Assyrian colony in Turkey, the tablets we’ve uncovered and the wood from a pair of ruined palaces match up well with the Middle chronology, somewhat plausibly with the Low, and very poorly with the Ultra-low.⁵ So despite the uncertainty, the Middle chronology is still in the lead, meaning Hammurabi’s reign was probably from 1792-1750 BCE.

4. The future of the past

One thing that fascinates me about archaeology compared to other sciences is that there’s a finite amount of data out there, and the questions you have may literally be unanswerable. We do still find new major sites every now and again, as well as new techniques for parsing our existing data. Maybe somewhere buried in the middle east, there’s the smoking gun to confirm exactly when Hammurabi ruled his empire. But unless and until we find it, everyone – historians, archaeologists, astronomers, and more – will keep working to solve what’s become quite a puzzle. Or, you might even say, a code.

Coming soon: Factorio is a zombie shooter for nerds

2 https://www.tertullian.org/fathers/dionysius_exiguus_easter_01.htm

3 Some scholars even argue that a sudden, complete collapse is the wrong framework. E.g: Guy D. Middleton, “Getting Closer to the Late Bronze Age Collapse in the Aegean and Eastern Mediterranean, c. 1200 BC.” (2024)

4 Huber, Peter J. “Astronomical Dating of Ur III and Akkad.” Archiv Für Orientforschung 46/47 (1999): 50–79. http://www.jstor.org/stable/41668440.