This reformed the confusing ancient Roman solar-lunar calendar, and is based on the Egyptian solar calendar. It was put into use in 709 AUC, and dates previous to this cannot be precise due to inconsistent usage of the leap-months in the old system. However, once put into place, the leap-day was used improperly at first, until Augustus Caesar fixed this problem. The early leap-years were every third year from 709 AUC until 745 AUC, and then none until 761 AUC and every fourth year thereafter.


  1. Januarius* - 31 days
  2. Februarius* - 28 days
  3. Martius - 31 days
  4. Aprilis - 30 days
  5. Maius - 31 days
  6. Junius - 30 days
  7. Quintilis** - 31 days
  8. Sextilis*** - 31 days
  9. September - 30 days
  10. October - 31 days
  11. November - 30 days
  12. December -31 days

*These two months were introduced to the Roman calendar in c. 38-80 AUC by Numa Pompilius. Previously, the useless days of winter were uncounted and the year began on 1 Martius.
**Renamed Julius in 710 AUC
***Renamed Augustus in 746 AUC

In leap-years, Februarius is given a 29th day, but for the purposes of festivals, the additional day is considered 24 Februarius, and festivals normally held from 24-28 are held from 25-29.

When numbering the days of a month, the Romans used a system that counted backwards to three specific days in the month:

Kalendae is the first day of the month.
Nonae is the ninth day before Idus, counting Idus itself as the first.
Idus is the fifteenth day of Martius, Maius, Quintilis, and October, and the thirteenth day of all the other months.

Thus, days were named:

The name of the Xth days varied, depending on the number of days in that month, and the placement of Idus.

The Julian calendar is often referred to as the Old Style by Western historians when converting dates to and from the Gregorian calendar.


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