The Romans used to refer to years by the names of the two consuls who were in office in each year. They kept lists of which men served as consuls. Romans were very confusing about dates - they used the terms "Ides", "Nones" and "Kalends", and counted the days backwards and inclusively before each of those days of the months. And if they used weeks at all, they were weeks of eight days, not seven.
In most other cultures, people referred to years as the "fifteenth . . (or whatever ).. of the reign of pharaoh X or king Y or emperor Z"
So you can imagine what a headache dates must be for historians of ancient times.