How to Read Greek Letter Additive Dates and Officina Numbers
It was not until after the age of Alexander that placing dates upon coins in the form of numerals became common. After the foundation of the Seleucid dynasty in Syria, many Syrian and other Eastern coins were dated according to the Seleucid era, which was computed from 1 October 312 B.C. The custom of dating according to an era became common in parts of Asia Minor and Syria in the second and first centuries B.C., and was continued under the Roman Empire. In Egypt, the Ptolemies usually dated their money by the regnal years of the king. Coins struck at Alexandreia under the empire were dated by the regnal years of the Emperor.
The mode of expressing dates is as follows:
Date numerals are often preceded by ETOUS (genitive case of ETOS = year in Greek), frequently written or abbreviated ETOYC, ET, or E.
Greek dates are also sometimes written out or abbreviated. Some examples follow (these are ordinal numbers):
ETOUS DEUTEROU = year 2 (of the second year)
The dates above may not be "proper" Greek. They are dates as actually written on Roman provincial coins minted in Alexandria and other cities.
To date a coin, you need to know the start date for the era. The eras in use at the various cities owed their origin to various circumstances. The local era of a city or province will often date from an important event in the history of the city, district, or province. The events that were the origin of many local eras are unknown. Sometimes the exact year from which an era started is also uncertain. Well-known and widely used historical eras include the following:
THE SELEUCID ERA. After the victory of Seleucus and Ptolemy over Demetrius at Gaza, B.C. 312, the former took possession of Babylonia. Hence the Seleucid era, in Syria and the neighborhood, was reckoned from October 1st, B.C. 312.
THE POMPEIAN ERA. In B.C. 64 Pompey, after the defeat of Tigranes, entered Syria. During the winter B.C. 64-63 he had his head quarters in Damascus and spent some months in organizing the affairs of Syria and reducing it to the condition of a Roman province.
THE CAESAREAN ERA dates from the victory of Caesar over Pompey at Pharsalia, Aug. 9th, B.C. 48. The city of Antioch, however, reckoned the commencement of the era from the autumn of the preceding year, B.C. 49, and other cities from slightly varying dates.
The start date of eras above and others are listed below:
If the era started before the common era (BC or BCE), to determine the common era (AD or CE) date, subtract the era start year from the date on the coin. If the result is less than zero, determine the date before the common era (BC or BCE) by subtracting the date on the coin from the era start year and then adding one.
If the era started in the common era (AD or CE), add the start year to the date and then subtract one to determine the common era date.
Letters of the Greek alphabet such as Α-Ν, standing for the months of the lunar year on the Athenian coins. On the series of Ptolemaic coins commencing with the era of ArsinoŽ II, Α-Ω (= 1-24) and ΑΑ-ΩΩ (= 25-48), etc., are not, dates but sequence letters.