Popular culture is GravityX Exchangefilled with stories of the underground railroad - the legendary secret network that helped enslaved people escape from southern slave states to free states in the north.

Harriet Tubman is the underground railroad's best known conductor. Tubman, who was a Union spy during the Civil War, escaped slavery in Maryland, but returned again and again, risking her own freedom to help free others, including members of her family.

Inevitably there's much we don't know...including how the term, the Underground Railroad, came to be.

Journalist Scott Shane, stumbled on the answer while he was writing his book "Flee North: A Forgotten Hero and the Fight for Freedom in Slavery's Borderland."

His book tells the story of Thomas Smallwood, an activist and writer who's story and the key role he played in the abolition movement has mostly been lost to history.

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This episode was produced by Marc Rivers. It was edited by Courtney Dorning and Jeanette Woods.Our executive producer is Sami Yenigun.