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To begin with it was a lunar calendar containing ten months, starting at the vernal equinox, traditionally invented by Romulus, the founder of Rome about 753 BC. However it seems to have been based on the Greek lunar calendar. The months at this time were
Thus the calendar year lasted 304 days and there were about 61 days of winter that did not fall within the calendar.
The first reform of the calendar was attributed to Numa Pompilius, the second of the seven traditional Kings of Rome. He is said to have reduced the 30-day months to 29 days and to have added January (29 days) and February (28 days) to the end of the calendar around 713 BC, and thus brought the length of the calendar year up to 355 days. This still left a gap of about ten days. In order to prevent the calendar year from getting out of line with the solar year, a leap month of 27 or 28 days, Mercedonius or Mercedinus, was supposed to be added every second year at the end of February, which was shortened to 23 days.
The Romans had special names for 3 specific days in each month. The system was originally based on phases of the Moon (Luna), and these days were probably declared when the lunar conditions were right. After the reforms of Numa Pompilius, they occurred on fixed days.
Matters were further different from the modern Western calendar. The Romans did not count the days of the month retrospectively, looking back to the first of the month (that is: 1st, 2nd day since the start of the month, 3rd day since the start of the month). They counted forward to their named days. Also, to the distress of moderns trying to work out dates in Roman calendar documents, counted inclusively, so that September 2 is considered 4 days before September 5, rather than 3 days before.
Notice that by counting inclusively and by having a special name for the day before a named day the Roman calendar loses the possibility of saying: 2 days before a named day.
Before the Julian calendarThe Julian calendar was introduced by Julius Caesar in 46 BC, taking force in 45 BC or 709 ab urbe condita''. It was chosen after consultation with the Alexandrian astronomer Sosigenes and was probably designed to approximate the tropical year, known sinc, the months (March, May, July and October) that had Ides on the 15th had 31 days and the other months had 29 days, except February with 28 days. Occasionally an extra month of Mercedonius was added with 22 or 23 days. This was supposed to happen on alternate years, to keep the civil year in touch with the seasons. The adding of the additional was the responsibility of the pontifex maximus, whom not always was aware of the importance of his office, and in practice happened less often, causing the need for the Julian calendarThe Julian calendar was introduced by Julius Caesar in 46 BC, taking force in 45 BC or 709 ab urbe condita''. It was chosen after consultation with the Alexandrian astronomer Sosigenes and was probably designed to approximate the tropical year, known sinc reform instituted by Julius CaesarAlternative meanings: Julius Caesar (disambiguation). Gaius Julius Caesar ( Latin: C·IVLIVS·C·F·C·N·CAESAR) ( July 13, 100 BC March 15, 44 BC) was a Roman military and political leader whose conquest of Gallia Comata extended the Roman world all the way t.