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Julian calendar
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Julius Caesar Interactive Gregorian calendar tool with fields for year, month, day, and era, set to December 8, 2025, and a blue Calculate button at the bottom.
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Julius Caesar
Julius Caesar Marble bust of Julius Caesar; in the Vatican Museums, Vatican City.

Julian calendar

chronology
Also known as: Old Style calendar
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History

Julian calendar, dating system established by Julius Caesar as a reform of the Roman republican calendar. By the 40s bce the Roman civic calendar was three months ahead of the solar calendar. Caesar, advised by the Alexandrian astronomer Sosigenes, introduced the Egyptian solar calendar, taking the length of the solar year as 365 1/4 days. The year was divided into 12 months, all of which had either 30 or 31 days except February, which contained...

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