How did April Fools' Day start and what are some famous pranks?

Historians aren't pulling your leg when they say no one is quite sure about the origins of April Fools' Day. 

April 1, the annual day of shenanigans, pranks, tricks and hoaxes, falls on Monday this year. While historians are unsure of the exact source of the tradition, they do know the custom goes back centuries, at least back to Renaissance Europe and possibly back to Roman times. Here's a look at what the experts say.