Julian Calendar

The new civic calendar introduced by Julius Caesar in 45 b.c.e. was revolutionary in that it ignored the moon. Earlier calendars in the Roman world had been based on the lunar phase cycle and had gotten badly out of step with the seasonal year. Remarkably, two key elements of our own modern calendar date all the way back to Caesar's innovations. The first is its division into twelve months, each with a fixed number of days, chosen so as to add up to the number of whole days in the seasonal year (365). The word month in this context is in fact a complete misnomer, since the divisions of our year are completely independent of the cycle of lunar phases. The second innovation was the concept of a leap year. By introducing an additional day once every four years, the average length of a year in the Julian calendar became 365.25 days, very close to the true length of the year.

The Julian calendar did not escape teething troubles. For over three decades an additional day was mistakenly inserted every third instead of every fourth year, necessitating a retrospective adjustment. Only by C.E. 8

was the pattern established that remains familiar today, whereby every fourth year (whenever the year is divisible by four) is a leap year.

The Julian calendar survived intact for over 1500 years in the Christian world, but (with the exception of Ethiopia) was eventually superseded by the more accurate Gregorian calendar. This happened at different times in different countries according to whether the dominant tradition was Catholic, Protestant, or Orthodox. Those who study calendrically related phenomena in medieval times, for example the orientations of medieval churches, have to be critically aware of the differences between the two calendars. See also:

Lunar and Luni-Solar Calendars.

Church Orientations; Gregorian Calendar; Roman Astronomy and Astrology. References and further reading

Aveni, Anthony. Empires of Time: Calendars, Clocks and Cultures, 111-115.

New York: Basic Books, 1989. McCready, Stuart, ed. The Discovery of Time, 88-89. Naperville, IL: Sourcebooks, 2001.

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