The calendar of Achaea is made up of twelve months of twenty-five days each. Although the calendar years are numbered from the fall of the Seleucarian Empire, and are marked AF (After the Fall), the months of calendar as we know them pre-dated the rise of Nicator.
The months of the Achaean calendar:
While this is the primary dating system of Achaea, other minor dating systems once existed and were in use by lesser known cultures. For instance, the Church itself used an internal dating system devised by the Archprelate Andariel.
Evidence also suggests that early in life of Humanity, the months of the year were named somewhat different, and the years were numbered from a system known as the Calliston calendar.