Time was important to the ancient peoples
The ancients were consumed with time. Accurate calculations were necessary so that the people knew when to plant, when to harvest and when to worship. They counted time by the rotation of the Earth, the phases of the moon and the sun as it changed elevation in the sky. This would all be well and good if it took a set amount of whole days for the earth to travel around the sun each year and a specific number of whole hours for the earth to spin on its axis each day. However, the time it takes for the Earth to rotate on its own axis and the time it takes for the Earth to make one rotation around the Sun are not whole days or whole hours and are not connected in any way to each other. The ancients were well aware of this discrepancy, however they all had different ways of dealing with the extra time, which amounted to a little less than six hours each year.
Why the calendar needs an adjustment
The Earth takes 365.2422 days to make a complete rotation around the Sun, so there is no way to calculate a year using whole days. The ancients lived their lives by what they saw in the skies. They planted when specific stars rose or set each season and by how many moon cycles they counted, so assigning a specific number of days to their year would cause confusion several years down the road. This was especially true if they used a lunar calendar to calculate a month. A lunar month is 29.5 days and a lunar year was only about 354 days, so what could the shamans do to make sure time was predictable? Some added festival days at the end of a year to catch up, others simply arbitrarily proclaimed the last month of the year to be as long as necessary to regulate the calendar. The Mayans, who were obsessive about time simply calculated it like a car's odometer and just kept an endless count of the days. Although their system was much more complicated than that, with Long Counts, katuns and bactuns, they had time calculated almost to the second. They were the Kings of Keeping Time.
Fixing the calendar
The Egyptians simplified their calendar a bit and simply added five days of feasting and celebrations ever so often to offset the difference. Julius Caesar decided he liked the Egyptian way of counting years so well, he decreed a 445 day long Year of Confusion in what we know as 46 BC to catch up. After that, he decreed the Leap Year every four years. However, this wasn't a perfect system either. If you add a day every four years, that's just a little too much and the whole system gets out of whack by a whole day every 128 years. By the time the 16th Century rolled around, it was pretty obvious that timekeeping needed tweaking some more. Everything was off by about ten days and that was giving the church headaches about when to celebrate their religious holidays, so Pope Gregory VIII decided to do something about it. First, he removed ten days from that year's October. Then he changed the way Leap Years were calculated. Leap Years that are divisible by 100 must be skipped unless they are also divisible by 400. This drops three Leap Days from the calendar every 400 years and that keeps things in balance. This new system was met with outrage, suspicion and stubborn resistance because Christmas was now celebrated on December 25th instead of January 7th. An interesting side-note was that Europeans always had hellebores blooming on Christmas Day before the Gregorian calendar was adopted. With the date pushed back, they were not blooming for Christmas and the people took it for a sign that the new calendar wasn't accurate. It took some countries well into the 19th Century to accept this new system of dating. The Gregorian Calendar now calculates the year length at 365.2425 days, which is only 30 seconds longer than the solar year. It will take 3,300 years for this to change the length of a year even one day, so we do not have much to worry about for the immediate future.
Fun Leap Year traditions
Now that all of the technical stuff is out of the way, there's lots of fun in a Leap Year. Did you know that in the 5th Century, the Irish woman Brigit, who later became Saint Brigid, convinced Saint Patrick that women should have the right to propose marriage to men. So, Saint Patrick deemed that the women could propose on each Leap Day, every four years. If the gentleman refused the proposal, he had to pay a fine and buy the lady twelve pairs of gloves to cover her ringless hands. However, in Scotland the proposal is considered null and void unless the woman wears a red petticoat. The man who turned down a proposal in Finland had to buy the woman enough fabric to make a skirt and there is a newspaper in France that only publishes an issue once every four years on Leap Day. The Greeks consider it unlucky to marry on Leap Day and of course, there are about 5 million people world-wide who have a birthday on February 29th. These people are called 'Leapers'. One of which is my cousin Richard, who was born in 1948 and is celebrating his 18th birthday today! However you choose to celebrate this extra day, just remember to have fun and enjoy it.