Mathematics Throughout History

Math and Calendars in History

What was the Roman calendar?

According to legend, the first Roman calendar appeared when Rome was founded, about 750 B.C.E. When it actually started is still up for discussion, and it apparently changed many times. The calendar was based on the complexity of the solar-lunar cycles. At first, it had ten months, starting in March and ending in December; January and February were added as the calendar was modified. Politics entered into the determination of this seemingly ever-changing calendar, too, with certain officials deciding to add days whenever they desired, and even choosing what to name certain months.

By the time of Julius Caesar (100-44 B.C.E.), Roman calendar-keeping was a mess. Caesar decided to reform the Roman calendar, asking help from astronomer and mathematician Sosigenes of Alexandria (first century B.C.E.; not to be confused with Sosigenes the Peripatetic [c. 2nd century], an Egyptian philosopher). The year 46 B.C.E. would have 445 days—a time appropriately called “the year of confusion.”

Sosigenes began the reformed year on January 1, 45 B.C.E., a year with 365 days, and proposed an additional day for every fourth year in February (leap day). The months January, March, May, July, August, October, and December had 31 days; the other months had 30 days, except February with 28 or 29 days (leap year dependent). And also in the Julian Calendar, there was only one rule: Every year divisible by 4 was a leap year.

The vain heir to Caesar, Augustus Caesar (63 B.C.E.-14 C.E.; a.k.a. Gaius Octavius, Octavian, Julius Caesar Octavianus, and Caesar Augustus), would change the Julian calendar in a several ways. Not only did he name the ninth month after himself, but he would change the number of days in many months to their present usage, adding more confusion to the calendar.

The Julian calendar would govern Caesar’s part of the world until 1582. Not that the Julian year was perfect: A year’s 364.25 days was too long by 11 minutes 12 seconds. Although the difference between today’s measurement of the year and the Julian year was not great, it adds up to 7.8 days over 1,000 years. But as with many decrees and mandates, Caesar, Sosigenes, and Octavian left it up to future generations to fix the problem.


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