Monday is Presidents Day, but it's more than just an excuse to skip work. It's an observance honoring all 44 presidents of the United States, pinned to the birthdays of two of the greats: George Washington and Abraham Lincoln. 

The Presidents Day tradition first began in 1800, the year after Washington died. People mourning the late leader celebrated his birthday, and in 1879 the holiday became official. It became a federal event in 1885 and was the first observance for a single individual, according to the History Channel. But the day wasn't just for Washington for too long — by the 1960s, Congress was requesting the government add Lincoln to the annual festivities. (Washington and Lincoln were both born in February.) Today, people use it to remember all of the U.S. commander-in-chiefs.

Read on for more Presidents Day facts, collected from sources like Mashable, the Huffington Post and the Smithsonian:

Washington's birthday was Feb. 22, 1732. He became president in 1789.

Lincoln's birthday was Feb. 12, 1809. He became president in 1861.

Washington did have fake teeth, but they weren't wooden, as lore has it. More likely, the teeth were made out of ivory.

The land where Washington was born is a national monument, while Lincoln's cabin is a national historical park. 

Lincoln's national historical park has a building with 56 steps — one for each year he lived before being assassinated.

Warren G. Harding had size 14 feet.

Martin Van Buren is responsible for the popular use of the term "OK."

Theodore Roosevelt had a ring with some of Lincoln's hair inside it.

Washington didn't want to be paid a salary for his work as president.

The first president to live part of his term in the White House was John Adams.

Washington had two spies.

Rutherford B. Hayes was wounded four times in battle during the Civil War.

James Madison attended Princeton University before it was called that; it was the College of New Jersey.

James Buchanan is the only president to not have a wife. Grover Cleveland started at the White House single but got married in office.

Lincoln was the first president to have a beard.

Two presidents have been impeached: Andrew Johnson and Bill Clinton.

Franklin Roosevelt was the first president to ride in an airplane.

The infection that killed Zachary Taylor began after he ate a bunch of cherries.

Barack Obama has two dogs, Bo and Sunny. Bo has a brother named Rico.

Bill Clinton plays the saxophone.