In order to determine the exact date of the battle of Ammaus, it is necessary to clarify the time of the start of Antiochus Epiphanes’ great expedition to the eastern satrapies which preceded it. The exact chronology is vital for the reconstruction of the timetable of the various phases of the campaign conducted at Ammaus and its environs, and in its wake for the dating of the Beth Zur battle and the evaluation of its outcome.

In the primary sources the only direct data on the date of the expedition is the statement in I Maccabees that Antiochus Epiphanes set out in the year 147, on the eve of the battle of Ammaus, en route from Antioch to the Upper Satrapies (3.37). As the date relates to an external event, the Macedonian-Syrian version of the Seleucid calendar was the one applied. Thus that year began in autumn 166 b.c. and ended at the beginning of October 165.

The season when the expedition to the Upper Satrapies took place must be postponed to the second half of that year, that is, between the spring and autumn of 165 b.c., and probably to the last quarter, i.e. the summer of 165:

1. (a) Porphyry, quoted by Eusebius, states that Antiochus V served as co-regent together with his father for ‘one year and six months’ (FGrH 260, F32, para. 13).

2. […]