Scholars have been trying to pin down the dates that ancient Egypt's rulers reigned for more than a century. Lists of kings dating from the time of the Pharaohs, and a history of Egypt written in the third century BC by Egyptian historian and priest Manetho have given them a pretty good idea of the order of events in Egypt's Old, Middle and New Kingdoms, and how long each ruler was in power for. But fixing this relative history to any definite dates has been fraught with controversy.
Not any more though. A small team of scientists using radiocarbon dating on 211 plant-based samples have "independently corroborated a century of scholarship in just three years", according to lead researcher Christopher Bronk Ramsey (also known for studying the Shroud of Turin).
Previously the main source of evidence for matching the "floating chronology" of ancient Egypt's rulers with absolute dates was a few ancient astronomical observations from the Middle and New Kingdoms. But this left plenty of room for argument. Many of the celestial and lunar phenomena in question repeat at regular intervals, so it's often hard to be sure exactly which event an ancient writer is recording. To make matters worse, the exact timing of astronomical observations also depends on the location of the observer.
Bronk Ramsey and his colleagues dated samples from seeds, baskets, textiles, plant stems and fruits, held in various museums. (They avoided any mummified remains as these could be contaminated with material used in the mummification process, such as bitumen, which would mess up the dating.) In general their results have confirmed historians' consensus about what happened when, but in a couple of cases the analysis showed that events happened earlier than thought - for example Djoser, of the Old Kingdom, reached power between 2691 and 2625 BC, and the New Kingdom began between 1570 and 1544 BC. The results suggest that New Kingdom pharoah Rameses II, considered the greatest of the Egyptian kings, ruled between 1297 and 1273 BC, and King Tutankhamun held the throne between 1353 and 1331 BC.
Radiocarbon dating has long been possible, but generally only gives age measurements with an accuracy of 100-200 years, not too helpful for pinning down the exact timing of someone's reign. To narrow the range of error, Bronk Ramsey and his colleagues combined the results from their samples with information about radiocarbon activity in the Nile Valley region and from the historical chronology.
The complex statistical analysis that the researchers had to use may still leave historians something to argue about. But the paper, published in Science this week, is an important step forward for Egyptology as it will put the whole field on a more scientific footing. The analysis will also help historians to correlate what was going on in Egypt with events in surrounding areas where we already have radiocarbon dating information, for example Libya and Sudan.