Archaeologists believe Egypt’s large pyramids are the
work of the Old Kingdom society that rose to prominence in
the Nile Valley after 3000 B.C. Historical analysis tells
us that the Egyptians built the Giza Pyramids in a span of
85 years between 2589 and 2504 BC.
Interest in Egyptian chronology is widespread in both popular
and scholarly circles. We wanted to use science to test the
accepted historical dates of several Old Kingdom monuments.
One radioactive, or unstable, carbon isotope is C14, which
decays over time and therefore provides scientists with a
kind of clock for measuring the age of organic material.
The earliest experiments in radiocarbon
dating were done on ancient material from Egypt. Willard
F. Libby’s team obtained acacia wood from the 3rd Dynasty
Step Pyramid of Djoser to test a hypothesis they had developed.
Libby reasoned that since the half-life of C14 was 5568 years,
the Djoser sample’s C14 concentration should be about
50% of the concentration found in living wood (for further
details, see Arnold and Libby, 1949). The results proved their
Subsequent work with radiocarbon testing raised questions
about the fluctuation of atmospheric C14 over time. Scientists
have developed calibration techniques to adjust for these
|Project members collect samples.
In 1984 we conducted radiocarbon dating on material from
Egyptian Old Kingdom monuments (financed by friends and supporters
of the Edgar Cayce Foundation). We then compared our results
with the mid-point dates of the kings to whom the monuments
belonged (Cambridge Ancient History, 3rd ed.).
The average radiocarbon dates were 374 years earlier than
In spite of this discrepancy, the radiocarbon dates confirmed
that the Great Pyramid belonged to the historical era studied
In 1994-1995 the David H. Koch Foundation supported us for
another round of radiocarbon dating.
We broadened our sampling to include material from:
- The 1st Dynasty tombs at Saqqara (2920-2770 BC).
- The Djoser pyramid (2630-2611 BC).
- The Giza Pyramids (2551-2472BC).
- A selection of 5th Dynasty pyramids (2465-2323 BC).
- A selection of 6th Dynasty pyramids (2323-2150 BC).
- A selection of Middle Kingdom pyramids (2040-1640 BC).
We also took samples from our Giza
Plateau Mapping Project Lost City excavations (4th Dynasty),
where we discovered two largely intact bakeries in 1991. Ancient
baking left deposits of ash and charcoal, which are very useful
The 1995 set of radiocarbon dates tended to be 100 to 200
years older than the Cambridge Ancient History dates, which
was about 200 years younger than our 1984 dates.
The number of dates from the two projects was only large
enough to allow for statistical comparisons for the pyramids
of Djoser, Khufu, Khafre, and Menkaure.
There are two striking results.
First, there are significant discrepancies between the 1984
and 1995 dates for Khufu and Khafre, but not for Djoser and
Second, the 1995 dates vary widely even for a single monument.
For Khufu’s Great Pyramid, they scatter over a range
of about 400 years.
We have fair agreement for the 1st Dynasty tombs at North
Saqqara between our historical dates, previous radiocarbon
dates, and our radiocarbon dates on reed material.
We also have fair agreement between our radiocarbon dates
and historical dates for the Middle Kingdom. Eight calibrated
dates on straw from the pyramid of Senwosret II (1897-1878
BC) ranged from 103 years older to 78 years younger than the
historical dates for his reign.
Four of the Senwosret II dates were only off by 30, 24, 14,
and three years. Significantly, the older date was on charcoal
(see “old-wood problem” below).
Test results from Middle Kingdom pyramid (Senwosret II).
The old-wood problem
Ancient Egypt's population was restricted to the narrow confines
of the Nile Valley with, we assume, a sparse cover of trees.
It is likely that, by the pyramid age, the Egyptians
had been intensively exploiting wood for fuel for a long time.
Because of the scarcity and expense of wood, the Egyptians
would reuse pieces of wood as much as possible. Some of this
recycled wood was burned, for example, in mortar preparation.
If a piece of wood was already centuries old when it was burned,
radiocarbon dates of the resulting charcoal would be centuries
older than the mortar for which it was burned.
We thought that it was unlikely that the pyramid builders
consistently used centuries-old wood as fuel in preparing
mortar. The 1984 results left us with too little data to conclude
that the historical chronology of the Old Kingdom was wrong
by nearly 400 years, but we considered this at least a possibility.
Alternatively, if our radiocarbon estimations were in error
for some reason, we had to assume that many other dates obtained
from Egyptian materials were also suspect. This prompted the
second, larger, 1995 study.
Old Kingdom problem
If the Middle Kingdom radiocarbon dates are good, why are
the Old Kingdom radiocarbon dates from pyramids so problematic?
The pyramid builders often reused old cultural material,
possibly out of expedience or to make a conscious connection
between their pharaoh and his predecessors.
Beneath the 3rd Dynasty pyramid of pharaoh Djoser, early
explorers found more than 40,000 stone vessels. These vessels
included inscriptions of most of the kings of the 1st and
2nd Dynasties, but Djoser's name occurred only once. Did Djoser
gather and reuse vases that were already 200 years old from
tombs at North Saqqara?
In the 12th Dynasty, Amenemhet I (1991-1962 BC) left clear
evidence of this kind of recycling. He took pieces of Old
Kingdom tomb chapels and pyramid temples (including those
of the Giza Pyramids) and dumped them into the core of his
pyramid at Lisht.
Test results from 5th Dynasty pyramid (Sahure).
Three of the eight radiocarbon dates from samples taken at
our excavation at the Lost City are almost direct hits on
Menkaure's historical dates: 2532- 2504 BC. The other five
range from 350 to 100 years older.
Our radiocarbon results from the Lost City site suggest that
the dates on charcoal scatter widely, like those from the
pyramids, with many dates older than the historical estimate.
The inhabitants were very likely recycling their own settlement
debris during the 85 or so years that they were building pyramids.
It may have been premature to dismiss the old wood problem
in our 1984 study. Radiocarbon dating can only tell us when
a tree died, not when it was last used. Wood may lay around
for centuries before being burned, especially in a dry climate
Also, any living forest or stand of trees will have old trees and
very young shoots. Any individual tree will have old parts (the
inner rings) and very young parts (the outer rings and small branches).
Do our radiocarbon dates reflect the Old Kingdom deforestation
Did the pyramid builders exploit whatever wood they could
Or did they have to scavenge for wood to burn tons of gypsum
for mortar, to forge copper chisels, and to bake bread for
thousands of assembled laborers?
The giant stone pyramids in the early Old Kingdom may mark
a major depletion of Egypt's exploitable wood. This may be
the reason for the wide scatter and history-unfriendly radiocarbon
dating results from the Old Kingdom.
While the multiple old-wood effects make it difficult to
obtain pinpoint age estimates of pyramids, the David H. Koch
Pyramids Radiocarbon Project now has us thinking about forest
ecologies, site formation processes, and ancient industry
and its environmental impact—in sum, the society and
economy that left the Egyptian pyramids as hallmarks for all
The David H. Koch Pyramids Radiocarbon Project was a collaborative
effort of Shawki Nakhla and Zahi Hawass, The Egyptian Supreme Council
of Antiquities; Georges Bonani and Willy Wölfli, Institüt für
Mittelenergiephysik, Eidgenossische Technische Hochschule; Herbert Haas,
Desert Research Institute; Mark Lehner, The Oriental Institute and the
Harvard Semitic Museum; Robert Wenke, University of Washington; John Nolan,
University of Chicago; and Wilma Wetterstrom, Harvard Botanical Museum.
The project was administered by Ancient Egypt Research Associates, Inc.
Bonani G, Haas H, Hawass Z, Lehner M, Nakhla S, Nolan J, Wenke R, Wölfli
W. “Radiocarbon Dates of Old and Middle Kingdom Monuments in Egypt,”
Radiocarbon 43, No. 3 (2001), 1297-1320(24).