When did we start using the Julian calendar?

The Julian calendar, proposed by Julius Caesar in AUC 708 (46 BC), was a reform of the Roman calendar. It took effect on 1 January AUC 709 (45 BC), by edict. It was designed with the aid of Greek mathematicians and astronomers such as Sosigenes of Alexandria.

When did calendar start?

In 1582, when Pope Gregory XIII introduced his Gregorian calendar, Europe adhered to the Julian calendar, first implemented by Julius Caesar in 46 B.C. Since the Roman emperor's system miscalculated the length of the solar year by 11 minutes, the calendar had since fallen out of sync with the seasons.