Journal of the Asiatic Society 1953 (Letters)
In a modern system of dating we mention the current year the month of the year and the day of the month and mostly but not always the weekday. [...] This presupposes the fixation of (1) the era (2) the initial day of the year and (3) the lengths of the months. [...] This era was probably introduced by the Babylonian astronomers who felt the need of a continuously running era instead of the use of the years elapsed or current since accession to the throne of the reigning king (Regnal Years) which had been in vogue since the time of the Kassites (1700 B. C.). [...] Tarn remarks 'It used to be taken that wherever the names of Macedonian months occur the Macedonian form of the calendar (Graeco-Chaldean) was in use' but recently it has been strongly argued that the calendar in use in Seleucia was a mixed form with the Macedonian months but the Babylonian year and that this and not the Macedonian form of the calendar was the form used by Seleucia on the P [...] But it agrees with the method followed in contemporary Parthia which mentions the year usually in the Seleucidean Era rarely in the Arsacid Era the name of the month in Greek and the ordinal number of the day which range from 1 to 30.