The Roman Calendars borrowed part of their calendars from the early Greeks. The Roman calendar consisted of 10 months and 304 days. They have not taken to account of the remaining 61 days which fell in the middle of the winter, and just simply ignored them. The names of the 10 Roman calendar months are Martius, Aprilis, Maius, Junius, Quintilis, Sextilis, September, October, November and December.

King Nuna Pompilius replaced the calendar with that of a similar Greek calendar in which they derived the calendar in the first place. The calendar now had 12 months and 355 days. Months that originally had 30 days now had 29. Months of Januarius and Februarius were added. Januarius was added at the beginning and Februarius was added at the end, but over time Februarius was shifted after Januarius. Today, we still use this order with January and February as our first two months.

In Roman calendars, the year began on Martius 1, the day which new consuls were inaugurated.

The table of the Roman months with derivation of name and the number of days each month consisted is shown below.