One of the most popular theories has to do with changing calendars in the 1500s. According to this explanation, the new year had been traditionally celebrated at the start of spring. When France changed to the Roman calendar, the new year fell in January. Those who were slow to adopt the change, often people who lived in the countryside, became known as "April fools," according to the story.
Other historians have linked the trickster tradition to ancient European spring festivals where people dressed in costume to fool each other. As the holiday spread throughout Europe and to the Americas, pranks became a rite of spring. As the years passed, the pranks got bigger and bigger. Here are a just a few of the greatest April Fools hoaxes in history. (National Geographic)
The earliest April Fools’ Day hoax on record was in 1698, says Alex Boese, curator of the Museum of Hoaxes. “People in London were told to go see the annual ceremony of the washing of the lions at the Tower of London,” he says. “They showed up at the Tower of London, but”—alas—“there was no annual lion-washing ceremony.”
The street prank worked so well that people kept pulling it year after year, targeting mostly out-of-towners.
“By the mid-19th century, pranksters had printed up fake tickets,” he says. “Hundreds or thousands of people would show up,” only to realize they’d been tricked.