RE: When Memes Get History Wrong (and some Roman History for You)

The Gregorian calendar was a reform of the Julian calendar. It was created around 1600 and named for Pope Gregory. It's basically the same as the Julian calendar, but it refined how they compute the leap year. Offhand, I think they added the rule that the leap year is ever 4 years unless it is divisible by 100 (but if it's also divisible by 400 then it is a leap year). They made the change because Easter had drifted pretty far away from spring.