Eras.
13. No method of computing time was adopted generally in antiquity. Each nation, each state, had its own era: yet, in the explication of ancient history, there is an evident necessity that some common era should be fixed upon, by which a synchronistic view of the various events may be obtained. For this purpose, the years may be computed either from the creation of the world, or before and after Christ. The latter method has the advantage not only of greater certainty, but also of greater convenience.
Of the various modes of computing time, the best known are those of the Greeks and the Romans; the former by olympiads, the latter by years from the foundation of Rome. The era of the olympiads commences at B. C. 776; that of the foundation of Rome commences at B. C. 753, according to Varro; at B. C. 752, according to Cato.—The era of the Seleucidæ, in the Syrian empire, commences with B. C. 312.—Various other eras, such as that of Nabonnassar, commencing with B. C. 747, are founded on observations preserved by Ptolemy, and made known by Scaliger, in his Doctrina Temporum.
Chronology constitutes a distinct science: the best introduction to which will be found in:
† J. C. Gatterer, Epitome of Chronology. Gottingen, 1777. A most excellent criticism on the ancient eras has lately been communicated to the public by:
† L. Ideler, Historic Researches into the Astronomical Observations of the Ancients. Berlin, 1806.
† D. H. Hegewisch, Introduction to Historical Chronology; 1811. A very useful and portable work.
[In English we have the laborious work of Dr. Hales:
Hales (Willm.) New Analysis of Chronology, explaining the History and Antiquities of the primitive Nations of the World, etc. Lond. 1809-12, 4 vols. 4to. New edition, corrected and improved, 1830, 4 vols. 8vo.
Blair's Chronology and History of the World, from the Creation to the present Time. Lond. 1803, folio.