January and February are actually the eleventh and twelfth months of the year, not the first and second.
When the Roman calendar was first introduced in the eighth century B.C.E., it inaccurately contained only 304 days for a total of ten months: Martius, Aprilis, Maius, Junius, Quin-tilis, Sextilis, September, October, November, and December. The names of the last six months were taken from the Roman words for five, six, seven, eight, nine, and ten.
In 452 B.C.E., when the months started to slide out of sync with the seasons, Roman ruler Numa added the month of January at the end of the year and the month of February at the beginning of the year. To make the calendar match the solar year, he decreed that the month of Mercedinus (with 23 days) be inserted between February 23 and 24 every other year. Four hundred years later, the calendar had slid so far out of sync that winter began in September. In 46 B.C.E., Roman emperor Julius Caesar, advised by astronomer Sosigenes, dropped the month of Mer-cedina and gave each of the remaining twelve months 30 or 31 days, except for February, which he gave 29 (adding a thirtieth day to February every fourth year). Caesar realigned the new Julian calendar with the seasons by adding an extra eighty days to the year as 46 B.C.E., which the Romans dubbed “the year of confusion.”
Unfortunately, the Julian calendar, while nearly accurate, was off by twelve minutes. The Romans figured a year had 365.25 days, but in reality, a year has 365 days, 5 hours, 48 minutes, and 46 seconds. By 730 C.E., a monk realized that this slight inaccuracy (eleven minutes, fourteen seconds) had caused the calendar to fall 5.5 days behind the change in season. He tried to make adjustments, but nobody listened until 800 years later. In 1582, Pope Gregory XIII corrected the mistake by shortening October 1582 by ten days and decreed that February would have an extra day each fourth year except in century years that could not be divided by 400 (such as 1700). England and its colonies (including America) did not adopt the Gregorian calendar until 1752, by which time the calendar was off by eleven days. Russia did not change to the Gregorian calendar until 1918.