Courtesy of Curiosity.com:
Thirty days hath September, April, June, and November; all the rest have thirty-one … except for February, for some reason. How did this poor month become the runt of the calendar, anyway? Blame the Romans and their weird superstitions.
Way back in the early days of ancient Rome, months weren’t really a thing. Anybody paying attention could feel when the seasons changed and see when the sun came up in the morning and went back down at the end of the day. Legend has it that the maybe-mythical founder of Rome, Romulus, decided there was a need for a calendar. Citing the growing number of festivals and activities throughout the year, he needed some sort of way to keep track of what was happening when. Thus, the 10-month Roman calendar was born. This lunar calendar began in March with the spring equinox and ended in December. The days left out? Well, that harvest-less chunk of time was pretty useless anyway.
After a few years on this schedule, the season started to fall out of sync (it only accounted for 355 days, after all). Romans threw in an entire leap month every once in a while — Mercedonius — to sync it back up. To make matters even more confusing, sometimes politicians would decide to throw in extra leap months, or nix leap months, to prolong their time or cut another’s time in office. It was a mess. By the time Julius Caesar came into power in 49 BC, he was fed up with this confusing garbage. Time for another calendar makeover!
Caesar killed the leap month in favor of moving to a sun-based calendar, like the Egyptians had, instead of a moon-based one. (To get things back on track, the year 46 BCE was 445 days long.) He added in extra days to the calendar year so that the year averaged out to 365.25 days, very close to the actual average length of a year: approximately 365.2425 days. The leap month became a leap day that was tacked on to February every few years, and the calendar was finally a sensible schedule. Oh, until Pope Gregory shuffled it around again, but that’s a tale for another month.”