Coptic calendar Roman Emperor Augustus imposed the Decree upon Egypt as its official calendar (although it was unsynchronized with the newly introduced Julian calendar which had erroneously been intercalating leap days every third year due to a misinterpration of the leap year rule so as to apply inclusive counting). To distinguish it from the Ancient Egyptian calendar, which remained in use by some astronomers until medieval times, this reformed calendar is known as the Coptic calendar. Its years and months coincide with those of the Ethiopian calendar but have different numbers and names. The Coptic year is the extension of the ancient
Leap year In 1825, Ideler believed that the lunisolar calendar was abandoned about 450 BC by the decemvirs, who implemented the Roman Republican calendar, used until 46 BC. The days of these calendars were counted down (inclusively) to the next named day, so February 24 was "ante diem sextum Kalendas Martias" ("the sixth day before the calends of March") often abbreviated a. d. VI Kal. Mart. The Romans counted days inclusively in their calendars, so this was actually the fifth day before March 1 when counted in the modern exclusive manner (not including the starting day). The Republican calendar's intercalary month was