If the reader is up-to-date on archaeological matters, he may expect a short, snappy answer to all the problems of chronology: carbon 14. He would be mistaken, on two counts: there is nothing short or simple about the radiocarbon process, or its applicability to historical problems; and, in fact, it did not solve the major chronological questions about dynastic Egypt. The process is certainly fantastically useful in other parts of the past, particularly in those very remote eras that are the province of the archaeologist-anthropologist rather than the archaeologist-historian. But in the case of Egypt, the previously established dating system helped to establish the validity of the carbon 14 process rather than the reverse.
The savage reader (to plagiarize Mark Twain) may reasonably ask at this point, “Why talk about it, then?” There are several good, logical answers to the question. One is that the radiocarbon process is very useful in dealing with Egyptian prehistory; another is that carbon 14 is only one of a number of related methods, the great gift of the physical sciences to history, which deserve a more than cursory treatment. But the real reason I want to discuss carbon 14 is because it delights me by its inherent improbability. Eighty years ago, the suggestion that a physicist could tell an archaeologist the age of a piece of wood by purely physical, laboratory techniques would have struck said archaeologist as completely preposterous. This is the real excitement of archaeology, and of life in general: that the horizon of what may be known is not bounded by what is known. And, of course, the development of the radiocarbon process is a fascinating intellectual adventure in itself.
In 1945, Willard F. Libby of the University of Chicago was studying the effect of cosmic ray neutrons upon the nitrogen of the atmosphere. The result of the meeting was a genuine, if tiny, nuclear reaction; the product was radioactive carbon. Libby argued that since its chemical behavior is the same as that of ordinary carbon, this carbon 14, or radiocarbon, should form carbon dioxide molecules and mix in with the ordinary carbon dioxide of the atmosphere. Every high school student of biology knows that carbon dioxide is taken in by plants in the process of photosynthesis. Since animals live off plants, the conclusion was logical, though rather startling: all living matter should be weakly radioactive, from the tiny proportion of carbon 14 that it absorbs.
The first verification of Libby’s theory came from a decidedly inglorious source—the methane gas given off by the city of Baltimore’s sewage. Not only did this decaying organic material give off radioactivity, but it contained exactly the proportion of carbon 14 that Libby had predicted. Subsequent tests were performed on samples of wood, oil, and other material from all over the world. The proportions were as predicted.
This was a good confirmation of the theory, but it was more than that. Libby immediately saw the possible application of the process to dating. Among his samples had been wood from the tombs of Snefru and Djoser, kings of the Fourth Dynasty. The dates given by radiocarbon checked out with the calculations Egyptologists had made independently.
How does it work? Obviously the laboratory apparatus did not contain a neon coil that lit up and read 4,500 years. Before the laboratory results could be translated into years of time, a lot of work had to be done.
Let’s take a specific organic object as an example—an oak tree, perhaps. When the tree died, it of course stopped taking in carbon 14. As it lay in the earth, or in the walls of a building in the form of planks, the radiocarbon it contained at its demise, being unstable, began to disintegrate. Libby calculated that the rate is about one percent each eighty years. The process of decay is exponential; that is, in the first eighty years one percent of the total decays, in the next eighty years one percent of the remaining total, and so on. Scientists talk about decay rate in terms of its “half-life”—the length of time it takes for half the original radioactive content to decay. At the latest measurement, the half-life of carbon 14 is 5,568 years.
Thus, by measuring the amount of carbon 14 remaining in our oak tree, or any piece of it, we can calculate (and if that sounds simple, it is not) how many years have passed since the tree stopped living. Truly, the process is brilliantly conceived. But it has certain limitations.
These limitations arise from various causes. One is the problem of the increase of error. You may have seen radiocarbon dates given in various publications; they look something like this: 3,325 years + - 150. The “plus or minus” indicates the range of possible error. The older the date given, the greater the range. Why the lack of precision? Well, for one thing, it is very difficult to get an uncontaminated sample, free of modern organic substances. If the sample we are working with is fairly recent in age, it still contains a large part of the original radiocarbon; hence, the intrusion of a chunk of modern carbon 14 represents only a small proportion of the total and does not affect the results too much. But if our object is thirty thousand years old, it has lost all but a tiny amount of the carbon 14 it contained at its demise; the amount is so small that it is hard to detect, even with precise laboratory instruments, and any intrusion, however minute, affects the results enormously. The problem of contamination was a serious one at first, when the process was new and unfamiliar; field-workers packed samples in straw or allowed bits of root from living trees to get into the container. Another source of contamination is the atmosphere itself; laboratory instruments must be carefully shielded against cosmic rays and must themselves be completely free from radioactive contamination. The composition of the atmosphere has been changed in the past century, not so much by atomic explosions as by the “old” carbon released by the combustion of coal and oil since the Industrial Revolution.
All these factors affect the accuracy of radiocarbon dates. Then there is the pleasingly mysterious “systematic uncertainty,” the causes of which seem to be unknown, which gives errors of one hundred to two hundred years. Further limitations come from the fact that only certain materials are suitable for processing. Charcoal and well-preserved wood are best; bone, for various reasons, has given unsatisfactory results. The sample must be burned to be tested, which means that choice specimens are not readily relinquished. And, because of the rapid (in geologic terms) decay rate of carbon 14, the process cannot be used with any material that is over 70,000 years old. This is plenty long enough from our point of view, but it frustrates archaeologists who work with fossil man and his immediate ancestors.
Several other physical techniques are employed in chronology. Thermoluminesce analyzes the decay of certain elements in pottery. Dendrochronology counts tree rings, and in some parts of the world scientists have constructed overlapping series of such rings which cover extended periods of time. Both techniques have their limitations, which I do not intend to discuss. Suffice it to say that although they have been of some use in establishing prehistoric chronology, their use in the dynastic periods of Egypt is limited. By the time these techniques were developed the chronology had already been fairly well established—though like everything else in Egyptology, it is constantly being revised.
One of the people who worked on chronology back at the beginning of the present century was James Henry Breasted, who is arguably the United States’s most famous Egyptologist. Born in the small midwestern town of Rockford, Illinois, Breasted had a long way to go to get to Egypt. In his day it was essential for an Egyptologist to study in Berlin, where the monumental figure of Adolf Erman was placing the Egyptian language on a sound philological basis for the first time. Breasted’s family was not wealthy, but he got to Berlin, and later to Egypt. Like Petrie, the American Egyptologist was a man of tremendous energy, but his talents lay in philology and administration rather than in excavation. His History of Egypt is still a wonderful read, though his interpretations are out-of-date. Breasted’s magnum opus was the translation of every known historical text from Egypt; the result fills five thick volumes, and required the personal inspection and copying by Breasted of almost every text included—many of the pre-Breasted copies of inscriptions look as if they were made at twilight by a myopic scholar who had lost his glasses.
The book, Ancient Records of Egypt, is Breasted’s great work in terms of published material, but many would say that his true monument is an institution, not a book. This is the renowned Oriental Institute of the University of Chicago, the first department for the study of Egyptology on American soil. Its expeditions have worked for many years in other parts of the Near East as well as in Egypt, and its publications number in the hundreds.
The first volume of Ancient Records contains a lucid summary of basic methods of Egyptian chronology. These methods have been refined since Breasted’s time, but the essential sources remain relatively unchanged.
The nearest thing to a contemporary history of Egypt we possess is the work of an Egyptian priest named Manetho, who wrote and lived under Ptolemy II Philadelphus, in the middle of the third century B.C. “Possess” is a misleading term, for we do not have the text of Manetho’s history. What we have are quotations and synopses made by later historians of Roman times. The quotations come mainly from Josephus, a Jewish historian who was trying to make a case for the antiquity of his people; the superior attitude of his Greek fellow scholars had riled him. Josephus is a biased source; he had an ax to grind, and even if he was too honest to misquote consciously, his bias would probably affect his choice of material.
The other sources merely summarize Manetho, giving lists of kings and sometimes a sentence of description. The copies do not always agree with one another, and they garble names and dates most horribly. How much of the error is due to the copyist, and how much to Manetho himself—who was, after all, a long way in time from the beginnings of Egyptian history—we do not know. But we know that Manetho is not to be trusted blindly, at least not in the copies we have. Speaking of dynasties, we should note that they are derived from Manetho, who was trying to distinguish separate royal houses or families. In view of the fact that Manetho is damned with such faint praise, one might ask why we rely on him for this breakdown. The answer, as most Egyptologists admit, is because Manetho’s concept has been used for so long that it would be inconvenient to discard it. His dynastic breakdowns work well enough, though in some cases it is hard to see why he started a new dynasty when he did.
Painstaking archaeological spadework and the study of hieroglyphic inscriptions have enabled scholars to check Manetho’s list of kings against contemporary records, and to construct lists of their own that sometimes differ drastically from the Greek’s. By the time of the Middle Kingdom the Egyptians were dating events by the years of a king’s reign. If a mass of dated objects gives year 23 as the last year for a particular monarch, we assume that he probably ruled no longer than twenty-three years. The records are fairly complete for the later period of Egyptian history; so, counting back from 525 B.C., when the Persians invaded Egypt, we can estimate the length of the later dynasties with fair accuracy.
Records from the earlier dynasties are still fragmentary. The Old Kingdom, which includes Dynasties One through Six, was followed by a period of confusion, when the country broke apart into smaller units ruled by local princes, some of whom continued to claim the titles of pharaoh. This First Intermediate Period, as it is called, causes chronological problems because dynasties Seven through Eleven, which comprise the period, were, in some cases, overlapping or contemporaneous. By the end of the Eleventh Dynasty the kingdom was again united under kings who kept good records. This is the Middle Kingdom, which includes dynasties Eleven and Twelve. Another period of disunion followed the Twelfth Dynasty, and again there is disagreement about the length of dynasties Thirteen through Seventeen. The Eighteenth Dynasty marks the beginning of the New Kingdom, or Empire, as it used to be called; documentary evidence from this period is good, but here the chronological problem is confused by possible coregencies, which have provided Egyptologists with some of their most exciting and inspiring sources of argument. There are other chronological confusions between the end of the Nineteenth Dynasty and the end of Egyptian history proper, so we cannot simply add up the known years of various kings’ reigns to find out when the First Dynasty began. Fortunately, there are other methods.
Everybody knows that the Egyptians invented the calendar. However, this is one of the pleasant oversimplifications that appear in high school history books; the Egyptians had not one calendar, but several. Probably the earliest was a lunar calendar whose months ran from one new moon to the next. A number of “primitive” peoples have lunar calendars, since the changes in the phases of the moon are conspicuous; but in Egypt the rhythmical activity of the river soon suggested another method of dividing the year—a division into seasons. One of these seasons was called “Inundation,” and the rise of the Nile at the beginning of the annual flood was an event eagerly awaited and anxiously noted. During the third millennium B.C. an event of quite a different character occurred at about the same time as the beginning of Inundation—the reappearance after a period of invisibility of the brightest star in the heavens. Sirius, the Dog Star, which the Greeks called “Sothis,” came to be regarded as the harbinger of the Inundation, and its heliacal rising was named wp rnpt, the “Opening of the Year.”
The lunar calendar worked admirably for a simple agricultural people; but as society became more complex, it was seen to have disadvantages. Every new month had to be established by observation, and no one knew in advance whether it would have thirty days or twenty-nine. At the end of the lunar year there would be a space of days, even weeks, before the opening of the new year, which was signalized by the rising of Sirius. So some busy bureaucrat decided, with royal approval, to set up another year whose exact length would be known in advance. This is called the “civil calendar,” and it is the distant ancestor of the one we use. It had twelve months of thirty days each, with five “intercalary” days at the end of the year. We don’t know how this unknown genius arrived at the number 365; he might have counted the days between successive risings of Sirius or he might have averaged out the number of days that elapsed between Inundations over a period of years.
Even this solution to the problem of time has a difficulty, which the reader has probably noticed. The true solar year does not have 365 days, but 365 and a quarter and then some. Hence, if the “Opening of the Year” occurred on day one, month one, when the civil calendar was first set up, four years later it would fall on day two, month one. A period of 1,460 years (four times 365) constituted what we call a “Sothic cycle” and brought the rising of Sirius back to “day one, month one” of the civil calendar once again.
There’s a lot more one can say about the calendars of ancient Egypt, but I am not that one. What really matters for our purpose is the Sothic cycle. From time to time the Egyptians saw fit to mention the rising of the Dog Star in connection with a date of their civil calendar. Now we know, from Roman sources, that a Sothic cycle—the coincidence of the rising of the star and the first day of the civil calendar—began in A.D. 139. By a simple process of arithmetic we can calculate that the previous cycle started in 1322B.C., and the one before that in 2782 B.C. (Bear in mind that there is no year zero.) We have a mention of a Sothic rising, with date, in the Twelfth Dynasty, and another in the Eighteenth. Hence we can establish these events in terms of our own time scheme with relative accuracy. Why not absolute? Because we don’t know where the observations were taken. It makes a difference. Still, the variance is only a few years one way or the other. Knowing the dates of the Twelfth and Eighteenth Dynasties enables us to fix the approximate length of the confused period between these two stable periods.
We do not have, as yet, any astronomical reference from the Old Kingdom. There are two major documents that attempt to give a king list, with dates, for the Old Kingdom. One of them is in pieces and the other is in fragments.
The fate of the Turin Papyrus is told in a story that may be apocryphal, but whose general spirit is unhappily too typical of the early days of archaeology. The papyrus was complete when it was discovered in 1823 by a gentleman named Bernardino Drovetti, who stuck it into a jar that he tied around his waist. He then rode off to town on his donkey. The gait of a donkey being what it is, Egyptologists have been pushing the pieces of the papyrus around ever since, and cursing Drovetti as they do so. The other document, the Palermo Stone, is equally fragmented, though its material would seem so much more durable. Several bits of it have been found, and the absence of the remainder is all the more frustrating because it gives year-by-year accounts of events for every king of the first five dynasties.
If the reader finds the foregoing discussion confusing, let me assure him that I have simplified the various problems to a degree most Egyptologists would consider unscholarly in the extreme. There are several other king lists from later dynasties, but they aren’t complete, perhaps because they were never intended to be historical documents. Names like those of the so-called heretic pharaohs of the Eighteenth Dynasty are omitted. There are references to Egypt in various foreign documents, but the chronologies of these countries have their own internal problems. Even if we were able to pin down a specific year for the beginning of the First Dynasty, this would be misleading; the unification was more likely a process than a single event.
So, although most authorities agree that the Twelfth Dynasty began around 1985 B.C., they differ by as much as four hundred years when it comes to the beginning of the First Dynasty. However, the evidence seems more and more to confirm the date of approximately 3110 B.C.as the start of history in Egypt, so we may as well stick to that for the time being.
Which brings us back, in case you thought I’d forgotten, to Dynasty O. The Palermo Stone lists several kings preceding those of the First Dynasty, and certain fancy tombs at Abydos have been attributed to these individuals. They were not rulers of a united Egypt, so they can’t belong to the First Dynasty, which starts with Menes, the man who brought both parts of Egypt under a single ruler. Hence Dynasty O. I wouldn’t worry too much about it, if I were you.