Lafayette Square, where hundreds of protesters were cleared by force Monday night before President Trump’s walk to St. John’s Episcopal Church, was once bordered by “slave pens.” Hundreds of enslaved black people were held captive within sight of the White House.

John W. Franklin, senior manager emeritus at the Smithsonian’s National Museum of African American History and Culture, said he thought about the horrifying history of slavery in D.C. when the National Guard, Secret Service and U.S. Park Police used chemical gas, rubber bullets and batons against those protesting a modern form of brutality: the killing of unarmed people of color by white police officers.

Enslaved people helped build the White House. At least eight of the first 12 presidents brought enslaved people with them to labor at 1600 Pennsylvania Ave., according to the White House Historical Association.

“We know about the construction of D.C., but we don’t know who built it, where the slave markets were? Where the slave quarters were? Did you know the site of National Archives is where the D.C. Central [Slave] Market was located on 7th Street? We know Arena Stage on the Wharf, but do we know that is where all the slave ships came in?” said Franklin, the son of renowned historian John Hope Franklin and the grandson of Buck Colbert Franklin, who survived the 1921 Tulsa Race Massacre, “99 years before Trump cleared Lafayette Square to walk to St. John’s. Enslaved people were kept in slave pens along Independence Avenue.”

Lafayette Square was one of hundreds of sites in the United States where enslaved black people were sold during 250 years of slavery, according to the GSA. The nation’s capital was a major hub for the slave trade.

“As the tobacco industry in the Upper South fell into decline, so did the need for large numbers of agricultural laborers,” according to the White House Historical Association. “Many slave owners decided to sell their enslaved workers to dealers based in Washington, D.C. These dealers imprisoned enslaved people in crowded pens for weeks or months before selling them to the Deep South, where the cotton industry had expanded exponentially.”

Lafayette Square is surrounded by historic buildings, some of which housed slave quarters.

Decatur House, which sits on the edge of Lafayette Square, “is one of only a few remaining examples of slave quarters in an urban setting,” according to the historical association. The house “is uniquely significant as the only remaining physical evidence that African Americans were held in bondage within sight of the White House.”

And in sight of the Capitol, too.

Solomon Northup, author of the memoir “12 Years a Slave,” was a free black man living in New York before he traveled to D.C., where he was kidnapped by slave traders in 1841 before being sold into slavery. In his book, Northup described the D.C. slave pen, where he was held and beaten with a whip.

“The building to which the yard was attached was two stories high, fronting one of the public streets of Washington. Its outside presented only the appearance of a quiet private residence. A stranger looking at it would never have dreamed of its execrable uses. Strange as it may seem, within plain sight of this same house looking down from its commanding height upon it, was the Capitol.”

Even St. John’s, the historic house of worship on the edge of Lafayette Square where Trump stood holding a Bible, has slavery in its past. The church was the site of several marriages and baptisms of enslaved black people, according the White House Historical Association.

Franklin once lectured in the basement of St. John’s. He urged listeners to walk to Decatur House, now the home to the historical association.

“Behind Decatur House, along H Street going west is a long, beige, two-story wall,” Franklin said. “Behind that beige wall are the slave quarters of that house.”

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