Tomorrow is the birthday of President Abraham Lincoln, one of the most memorialized leaders in American history.

There are statues and monuments and cities and schools named for him, and a story behind each one.

Here’s the story behind the Lincoln Memorial in Washington, DC.

Or, actually, the story of what’s underneath the memorial.

It’s called the Lincoln Memorial Undercroft, and it’s a result of the engineering it took to build the monument in that spot.

The U.S. Army Corps of Engineers had spent decades dredging and filling an area to the west of the Washington Monument.

Workers had to dig down 40 feet and then build huge concrete piers to support the marble that would eventually make up the memorial.

The foundation work alone took over a year.

Once the project was complete, people were focused on Lincoln’s stirring words on the walls of the open air monument, the stunning statue of the 16th president looking out at the Capitol and the Washington Monument.

They didn’t think much about the basement.

But around the time of the American Bicentennial, crews working on some renovations started looking into the lower level.

They spotted stalactites and stalagmites, and they noticed that some of the workers had actually left cartoon graffiti on some of the walls.

There were several stalled attempts to make something out of the space, but in 2017 the National Park Services decided to refurbish the Undercroft and open it up for public visits.

So the secret basement of the Lincoln Memorial may not be a secret for long.

Shortly after Abraham Lincoln died, a farmer in Takoma Park, Maryland, Samuel M’Closkey Fenton decided to honor the late president by carving his name into a beech tree.

Since there was more room, he decided to create a word grid, writing the name ABRAHAM LINCOLN over and over until there were nearly 200 characters in all.

He also added the names of the other presidents, but not as word grids.

Lincoln Memorial Undercroft (Atlas Obscura)

The Presidents’ Tree (Friends of Sligo Creek)

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