How do we know when the pharaohs reigned, and how sure can we be?

Egyptologists date the pharaohs by stitching together several imperfect clocks, and the answer is a consensus with error bars, not a certainty. The conventional chronology places the start of the Old Kingdom in the 27th century BC, the Middle Kingdom in the 21st and the New Kingdom in the mid-16th. Within that consensus, chronologies still diverge by about 300 years for the Early Dynastic Period, up to 30 years in the New Kingdom and a few years in the Late Period.

The backbone is the king-lists, which record how long each ruler reigned. But the surviving ones are either comprehensive with big gaps (the Turin King List) or complete but missing rulers (the Abydos King List and the Palermo Stone). A regnal year inscribed on a monument gives only a minimum length of a reign, and some dynasties probably overlapped rather than ruling one after another.

Then come the cross-checks. Synchronisms with Babylon and other lands help: a stela from Byblos shows that the pharaoh Neferhotep I was contemporary with Hammurabi of Babylon. A famous astronomical clock, the Sothic cycle, uses the rising of the star Sirius against a 365-day calendar with no leap years, which slid by about one day every four years. In 1904 Eduard Meyer found six Sirius dates on which much of conventional chronology is based. But more recent research eroded confidence in it, and experts have moved away from relying on it.

Today radiocarbon dating checks the old dates. For the Early Dynastic period it narrows consensus, and a 2013 study found a First Dynasty start in the 32nd or 31st century BC. Not everyone accepts the mainstream: alternative chronologies, outside scholarly consensus, lower New Kingdom dates by up to 350 or 500 years.