Calendars have historically been a messy business. The earliest calendars were based on lunar cycles and seasonal patterns as a way of tracking time between planting, growth, and harvest of crops. The calendar that most people use today is called the Western or Gregorian calendar. The earliest "draft" of this calendar, if you will, was introduced by Romulus, the first king of Rome. The Calendar of Romulus began in March and had only ten months of thirty or thirty-one days. This was intended to be helpful in keeping track of agricultural seasons, but the gap between December and March was certainly a problem! A later king, Numa Pompilius, decided to change things up a bit. He added the months of January and February to the calendar so that there might be a running yearly cycle of months, and he changed the number of days in many months so that some had twenty-eight, some twenty-nine, and some thirty-one. Even with these changes, the calendar was still about ten days short of a solar year, and eventually this way of tracking time fell out of sync.
For a long time, the calendar was pretty unruly in Roman territory. Many changes were proposed to the existing calendar, but it was not until the year 46 BCE that Julius Caesar proposed a better, standardized calendar. The Julian calendar is made up of three-hundred and sixty-five days organized into twelve months. In the Julian system, all months except for February had thirty or thirty-one days. Unfortunately, February remained and remains one of those short-cut months that didn't fit cleanly into the calendar. This calendar also introduced the leap year as a means of making up time that did not otherwise fit into the cycle of time.
As time went on, the Julian calendar, too, fell out of sync with the natural world. The Gregorian Calendar was introduced in 1582CE as a replacement for the Julian, which did not accurately reflect the solar year. The reason February has only twenty-eight or twenty-nine days today is thanks to this long, messy history of keeping track of time!