Finally tonight, part three of our series Hidden Histories.

Across the United States, the legacy of slavery can still be seen on university campuses and at the homes of slave owning presidents.

But what about the enslaved people who built them?

Tonight, we tell you about a man who helped create some of America's most well-known monuments.

Some of Washington, D.C.'s most familiar landmarks were built with the labor of enslaved people, their accomplishments largely lost to history.

Historian Sarah Fling of the White House Historical Association has researched their contributions.

What would Washington look like if not for enslaved labor?

SARAH FLING, White House Historical Association: Washington, D.C. is absolutely built on the backs of enslaved laborers.

The federal government considered them to be a cheap and bountiful workforce, especially when there weren't artisans living in the district of Columbia yet, as it hadn't really become a bustling city as it is today.

JOHN YANG: Fling says one of those enslaved laborers was Philip Reid, a trained sculptor who likely learned his trade from the man who enslaved him.

Charleston, South Carolina.

Sculptor, Clark Mills.

For an enslaved person, was that unusual?

JERMAINE FOWLER, Author, "Humanity Archive": There was a lot of enslaved craft people, actually.

John Yang: Jermaine Fowler is the author of the Humanity Archive.

Jermaine Fowler: When we think of enslaved artisans, they worked in nearly every craft in America, from furniture makers to iron workers to architectural artisans.

JOHN YANG: After President Andrew Jackson died in 1845, Mills won the commission to design a memorial.

KWASI HOPE, Historian: He claimed that he would build the first bronze statue in America.

He would cast it on site, and then he would also build the first statue ever in the world of a horse standing on his hind legs.

JOHN YANG: Historian Kwasi Hope.

KWASI HOPE: So when he won that bid, who did he bring with him?

Philip Reid.

JOHN YANG: Their sculpture still stands in Lafayette Square, across the street from the White House.

In 1860, Mills, again with Reid by his side, won another important commission casting the bronze statue of freedom to sit atop the U.S. Capitol dome.

So, Philip Reid, do we know what role he played in creating the statue of freedom?

SARAH FLING: So, we know for sure that he kept the fires under the molds for the bronze casting process of this 19-and-a-half-foot sculpture.

So this is certainly skilled labor that requires physical strength and also basic understanding of engineering.

JOHN YANG: By some accounts, Reid designed the pulley system used to hoist the statue to the top of the dome.

Other historians say no contemporary evidence supports that claim, but records like this pay voucher show that Reid worked nearly nonstop for almost a year at a wage of a dollar 25 a day.

KWASI HOPE: He was actually paid more than the craftsperson because he was just that talented.

But he didn't get to keep any of that money.

The only day he had a little bit of that money he could keep was Sundays.

And we still don't know he actually got to keep that money on Sundays.

JOHN YANG: After emancipation, Reid stayed in Washington and worked as a plasterer.

He changed the spelling of his last name from R-E-I-D to R-E-E-D, perhaps to mark his status as a newly freed man.

And the indignities that he faced in life did not end with his death?

SARAH FLING: The very first cemetery where he's buried closes a few years after his passing.

So he's decentered and moved out to Columbian Harmony Cemetery, a massive burial ground for African Americans in Washington, D.C. and several decades later, he's decentered again, because in 1960, all of those bodies are removed in order to eventually make room for the Rhode Island Avenue Metro Stop.

JOHN YANG: Despite his contributions, his final resting place is unknown.

JERMAINE FOWLER: I think that's one of the main reasons that these stories like this need to be recovered, to show that Black people had a very heavy hand, literally had a hand in the founding of the nation.

SARAH FLING: I hope that when people walk past the Capitol, either working here in D.C. or visiting his tourists, they remember this contribution that Philip Reid made to the symbol of freedom, even when he didn't have it himself.