The Julian calendar had 365 days, with an extra day added to the end of every fourth February. This lighthearted article suggests that Caesar’s idea for the Julian calendar was taken from his sojourn in Egypt. That makes sense, given that Egypt had the world’s best astronomers at the time, and they had likely figured out that a year was 365 and a quarter days from observing the sun carefully over many years. Caesar was looking to reform Rome’s political system, in which the calendar was subject to more or less arbitrary modification by the college of priests and the result was years which lasted more than 400 days followed by years of about 200 days, because the priests favored this consul over that one or the augurs needed to insert an extra month into the year when birds flew into the temple window on a particular day (really).
In fact, it is entirely possible that they figured out that a “year” was the amount of time it took a round earth to orbit the sun, not the other way around. Now in fact, the earth rotates on its axis 365.242374 times as it completes an orbit around the sun, which means that every twenty-fifth leap year, you don’t have leap year, except for centennial years that divide equally into 400. So 1900 was not a leap year, 2000 was a leap year, and 2100 will not be. And the rotation of the earth is slowing, at an unknown but detectable rate. It remains to be seen whether the rotation of the earth will slow down enough by the year 4000 to require someone to have to decide to make that year not be a leap year to make up for it. But that’s not exactly a problem we need to address today.
Famous people born on Leap Day include singer/golfer Dinah Shore, serial murderer Richard “the Nightstalker” Ramirez, motivational guru Tony Robbins, rapper Ja Rule, and lawblog king Eugene Volokh. Wikipedia claims that people born on February 29 can call themselves “leaplings” but I suspect that someone just made that up because I’ve never heard that term and it sounds pretty dorky. On February 29, 1504, Christopher Columbus accurately predicted a lunar eclipse and thus awed Native Americans into supplying his men instead of killing them.