For more than a century, one of Washington's best-kept secrets lay beneath the Lincoln Memorial: the Undercroft, a soaring 50,000-square-foot foundation built to keep the landmark from sinking into D.C.'s swampy ground.

Discover the history of the Lincoln Memorial in Washington, D.C.—from its design and 1922 dedication to its role in civil rights history, including Marian Anderson’s concert and Martin Luther King Jr.’s “I Have a Dream” speech.