What do mathematicians and pie fans have in common? A love for March 14.

Monday marks Pi Day.

For math lovers, it's a chance to celebrate Pi, one of the most important numbers ever, representing the ratio of a circle's circumference to its diameter.

Although Pi is typically rounded down to 3.14, it can go on forever. According to Guinness World Records, the most accurate value for Pi is more than 62 trillion digits (62,831,853,071,796 to be precise). It was calculated last August by the University of Applied Sciences in Switzerland.

For those who don't enjoy math, you get pie. Cherry pie. Apple pie. Pizza pie. All the pies.

Whether you calculate it or eat it, Pi (and pie) bring joy to many. Here's how it all started.

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The history of Pi

Pi has been around for 4,000 years, used by ancient Babylonians to calculate the area of a circle by taking three times the square of its radius, according to the Exploratorium, a San Francisco-based museum.

Early calculations of Pi were based on measurement until the Greek mathematician Archimedes became the first to use an algorithmic approach, according to PiDay.org, a website created to encourage learning in STEM subjects.

The Pi symbol was introduced in 1706 by mathematician William Jones, but it wasn't made popular until Swiss mathematician Leonhard Euler used it in 1737.

The Pi symbol is the first letter of the Greek word, perimetros, which loosely translates to “circumference,” says PiDay.org.

How did Pi Day start?

Former physicist Larry Shaw, who connected March 14 with 3.14, celebrated the first Pi Day at the Exploratorium with fruit pies and tea in 1988. The museum said Shaw led Pi Day parades there every year until his passing in 2017.

In 2009, the House of Representatives passed a resolution marking March 14 as National Pi Day.