“The origin of this era is thus represented by Syncellus, from the accounts of Polyhistor and Berosus, the earliest writers extant on Chaldean history and antiquities.ASC 23.2

“‘Nabonassar [king of Babylon] having collected the acts of his predecessors, destroyed them, in order that the computation of the reigns of the Chaldean kings might be made from himself.’ASC 24.1

“It began, therefore, with the reign of Nabonassar, Feb. 26, b. c. 747. The form of year employed therein is the movable year of 365 days, consisting of 12 equal months of 30 days, and five supernumerary days; which was the year in common use, as we have seen, among the Chaldeans, Egyptians, Armenians, Persians, and the principal Oriental nations, from the earliest times.”-Ib., vol. i., p. 268.ASC 24.2

As the year of this era is a fraction of a day less than a solar year, it would fall back of the true year one day in every four years, so that in the course of 100 years its commencement would be 25 days earlier in the solar year than at the commencement of that period; and after 1461 years it would fall back through all the seasons, and anticipate the solar time by an entire year. To reduce these to common years, it is therefore necessary to take into consideration this difference in their commencement. Chronological tables give their adjustment. Says Dr. Hales:-ASC 24.3

“The commencement of the era of Nabonassar, b. c. 747, is critically defined, both from history and astronomy.ASC 24.4

“1. Thucydides, b. 8, had preserved a curious original document, in the third treaty of peace concluded between Tissaphernes and Peloponnesians, beginning with its date: ‘In the 13th year of the reign of Darius, [II. Nothus,] etc.’ This treaty, it appears from the history, was made in winter, in the 20th year of the Peloponnesian war, which began in the spring, b. c. 431; and consequently the 20th year, in winter, was the beginning of the Julian year, b. c. 410; which, added to the 13th year of Darius, or 337th of the era, gives its commencement, b. c. 747.ASC 24.5

“2. Censorinus, in the valuable synchronisms mentioned before, states that the 986th Nabonassarean year began the 7th of the Calends of July, or June 25th, in the year a. d. 238, in which he published his work. Therefore that Nabonassarean year did not end till June 25 of the next Julian year, a. d. 238; which, subtracted from 986, gives the commencement of the era, b. c. 747.ASC 25.1

“3. According to Ptolemy, Hipparchus selected three ancient eclipses of the moon, out of those observed at Babylon, and brought from thence; of which the first happened in the first year, and the two others in the second year of Mardok Empadus, the fifth king in succession from Nabonassar. This proves, decisively, that the era of Nabonassar was in established use before the time of Hipparchus, though he did not give the collected years from the beginning of the era. These, probably, were not reckoned up in the original Chaldean Era, which only marked the succession of kings, and the number of years which each reigned. The collected years might have been added afterwards by the Egyptian astronomers.ASC 25.2

“4. Ptolemy himself mentions a lunar eclipse of 7 digits, in the 7th year of Ptolemy Philometor, and 574th year from Nabonassar, which happened on the 27th of the Egyptian month Phamenoth, and lasted from the eighth to the tenth hour. In that year, the 27th of Phamenoth was the first of May. And, by astronomical calculation, there was a lunar eclipse of the 7 dig. 26 min., on May 1, b. c. 174, which lasted two hours fifty minutes; and this year, b. c. 174, added to 573 years complete, gives b. c. 747, for the commencement of the Era.”-Hales, vol. i., pp. 269-70.ASC 26.1

The historical catalogue of the reigns of the kings of the Nabonassarian Era, commencing with Nabonassar, is called Ptolemy’s Canon, from Claudius Ptolemæus, a celebrated Alexandrian mathematician, who continued the Canon down to his own time, a. d. 137. This ancient Canon,-of which three ancient MS. copies have been found, all of which entirely agree except in the spelling of some names,-gives the names, and the length of the reigns, of all the successive Chaldean, Persian, Grecian, Egyptian and Roman kings, from b. c. 747 to a. d. 137.ASC 26.2

“To the authenticity of these copies of the Canon,” says Dr. Hales, “the strongest testimony is given by their exact agreement throughout with above twenty dates and computations of eclipses in Ptolemy’s Almagest, recited by Jackson, as he himself acknowledges.”-Vol. i., p. 450.ASC 26.3

“From its great use as an astronomical era, confirmed by unerring characters of eclipses, this Canon justly obtained the highest authority among historians also. It has most deservedly been esteemed an invaluable treasure, ‘omni auro pretiosior,’ as Calvisius says, and of the greatest use in Chronology, without which, as Marsham observes, there could scarcely be any transition from sacred to profane history; and by means of it some important dates are supplied in sacred Chronology, that could not otherwise be ascertained. It fills up especially an important chasm, from the reign of Nebuchadnezzar to the reign of Cyrus, without which the term of the seventy years of the Babylonish captivity, ending with the latter, could not be easily adjusted.”-An. Chro., vol. i., p. 280.ASC 27.1

The Roman Era

The (Vulgar) Christian Era