Calendar Origins

The answers to many questions about calendars

Home <<Egyptian Calendar Roman Calendar Julian Calendar>>

Modern Calendar Origins:

Calendar Origins - Where did calendars begin?

Day Name Origins - Where did the Names of Days come from?

Calendar Name Origins - Where did the Names of Months come from?

Months of the Year Origin - Why 12 months in a year?

Why 28 days in February?

Who set the Year 0, AD, BC?

Calendars it Derived From:

Egyptian Calendar

Roman Calendar

Julian Calendar

Roman Calendar - Why 28 days in February?

We owe the modern calendar's differing number of days each month to the Romans. The early Roman calendar consisted of 12 months beginning in March like this (later January became the start of the year):

Month Length
Martius 31
Aprilis 29
Maius 31
Iunius 29
Quintilis 31
Sextilis 29
September 29
October 31
November 29
December 29
Ianuarius 29
Februarius 28
Februarius (leap years) 23
Intercalaris (leap years) 27/28

The early Romans attempted to syncronize the months with the first crescent moon following a new moon resulting in some months of 29 days and some of more.

Every other year, February was shortened and a leap month (Intercalaris) was added in an attempt to realign lunar cycles with the solar calendar. The lengths of the years in a four year cycle of this lunisolar calendar were 355, 377, 355, and 378 days. This added up to 4 days too many to stay in sync with the solar year.

Julian Calendar

Eventually Julius Caesar asked an astronomer, Sosigenes of Alexandria, Egypt, to devise a better calendar. What resulted is called the Julian Calendar. He abandoned aligning the months with lunar cycles, and adopted months of 30 or 31 days length, keeping February at 28 days. He introduced an extra day in February in leap years. Sound familiar?

Julius Caesar re-named the 5th month after himself. His successor, Augustus Caesar, re-named the 6th month after himself.

The first day of each month was called Kalendae, or calends. Debts were due on this day, so books to track payments were called calendarium (account book) from which we get our modern day calendar.

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