Il Canone di Tolomeo
Ptolemy’s Canon Fixed by Eclipses.
—The Greek-Egyptian astronomer Claudius Ptolemaeus, or Ptolemy, who lived near Alexandria in the 2d century of the Christian Era, wrote an astronomical work entitled Mathematike Syntaxis ("Mathematical Composition"). It is, however, better known by its Arabic title, the Almagest, because it was preserved for posterity by the Arab civilization that flourished during the Dark Ages, when Europe was sunk in ignorance of classical science and literature. This work, which was the authoritative treatise on astronomy for 1,400 years, until superseded by the theory set forth by Copernicus contains data for numerous eclipses and other celestial phenomena, dated to the year, day, and hour in the ancient Egyptian calendar. There are 19 eclipses, ranging over nearly 900 years, many of which are dated in regnal years of various kings.As a sort of appendix to the Almagest is Ptolemy’s Canon, or list, of kings, enumerating consecutive Babylonian, Persian, Macedonian, and Roman rulers, with the lengths of the reigns and the totals, thus furnishing a scale of years by which to reckon intervals between the observations mentioned in the Almagest (for the canon, see p. 154). Since its purpose was not to give a complete record of all the reigns, but to assign a regnal number to every year in the scale, it did not include any reign that lasted less than a year, and the reigns were counted by full years, ignoring the exact date of accession. The years by which it was reckoned were neither lunar nor true solar years, but the ancient Egyptian calendar year of 365 days, which wanders backward through the seasons one day every four Julian years (see Vol. I, p. 176). The starting point of the canon is the beginning of the first regnal year of the Babylonian king Nabonassar, a point that can be placed, by means of the exact intervals given in the Almagest between that point and the various eclipses, at noon Feb. 26, 747 b.c. This was the 1st of Thoth, the Egyptian New Year’s Day, at that time (although by Nebuchadnezzar’s time Thoth 1 had shifted to January, and by the time Ptolemy himself lived, it had moved back through the autumn and into July).
From Ptolemy’s Canon, then, it is possible to assign b.c. dates to any regnal year of any of the kings in the list, that is, the years as reckoned in the Egyptian calendar. In the early (Babylonian) period of the Canon of Ptolemy each Egyptian year began about one to four months earlier than the corresponding lunar year beginning with Nisan. This is shown by the way in which the Egyptian years, as fixed by the eclipse data of Ptolemy’s Almagest, are aligned with the Babylonian years as fixed in the tablet of the 37th year of Nebuchadnezzar and the similar tablet from the 7th year of Cambyses (which even records one of the same eclipses mentioned in the Almagest).
Ptolemy wrote many centuries after the early eclipses he records, and depended on copies of the astronomical documents from which his information was originally derived. Yet the canon is corroborated wherever it can be checked by ancient Babylonian, Persian, and Egyptian documents, showing that Ptolemy’s regnal numbering corresponded with the contemporary reckoning.
The canon dating harmonizes with the astronomically fixed 37th year of Nebuchadnezzar, although the Almagest does not mention that year. It agrees also with another eclipse in the preceding reign, and with three others in the reign of Mardokempad (Marduk-apal-iddin, or the Biblical Merodach-baladan), the earliest eclipse being only 26 years from the starting point of the canon. And since the number of years from this point back to the first year of Nabonassar agrees with the Babylonian Chronicle and the Babylonian King List A (both found on clay tablets), it can be considered settled that Ptolemy’s Canon gives us exact dates as far back as 747 b.c. Furthermore, both the Assyrian king lists and the Assyrian limmu list, sometimes called the Eponym Canon, are in harmony with Ptolemy’s reckoning of the lengths of the reigns wherever these lists for the close of the Assyrian Empire overlap the earlier section of the canon dating based on the eclipses. Since the complete canon is not easy to find in publications in English, a translation of it is included, for reference, on the next page.
Note.—The first three columns of the tabulation on the opposite page are a translation from the Greek text of Ptolemy’s Canon. The heading at the top of column 1, "Of the Assyrians and Medes," refers to kings of Babylon (some of the earlier ones were Assyrian rulers). After the Babylonian kings come "the Persian Kings," whose line ends with Alexander the Great. Then Ptolemy continues with a listing of the Macedonian rulers of the Egyptian division of the defunct empire of Alexander. The list carries on through the Roman emperors, presumably down to the date when Ptolemy lived. The second column gives the length of each reign. The third gives the accumulated total years of the era. Hence the number opposite any king’s name represents, in terms of the Nabonassar Era, his last year of reign. Thus for example, the figure 226 opposite Cambyses represents his 8th, that is his last, year. His year 1 is the year 219 of the canon, the year following the total figure for the preceding king, Cyrus. Accordingly, chronologists have referred to Cambyses’ first year as n.e. (Nabonassar Era) 219, and have used this n.e numbering throughout, but Ptolemy’s Canon gives only the cumulative total at the end of each reign, carrying that cumulative total down only to the end of Alexander the Great’s reign, and then beginning a new series of totals.
The last two columns, not in Ptolemy’s Canon, are added for convenience: the n.e. for the year 1 of each reign, and the b.c. date of Thoth 1, the beginning of each of these Egyptian years of the canon. Ptolemy used the old 365-day Egyptian calendar years, not the years used by the Babylonian, Persian, Macedonian, and Roman rulers, and not the Julian-Egyptian civil calendar as stabilized by Augustus to begin on Aug. 29 (30th every 4 years).
