Okay, Harriet Tubman, born into slavery in the early 1800s, escaped slavery, probably best known today for making 13 trips to the South and guiding 70 slaves on their escape to free states via a system of secret routes, sympathizers and safe houses referred to as The Underground Railroad. Tubman went on to serve as a spy for the Union army during the American civil war, and was a figure in the women's suffrage movement, surviving into the 20th century.

So, the fact that she was a black woman is kind of important to Harriet Tubman's lore, and casting Julia Roberts in the role is rather inappropriate.

The Underground Railroad had nothing to do with actual trains, but they used a lot of railroad related terminology as code speak. Trail guides were referred to as "conductors," safe houses were "stations," etc. Very little of it was actually underground; I'm sure a few slaves hid in root cellars or caves along the way, but there were no tunnels. Escapees were sometimes carried by boat or train but most traveled on foot and/or by wagon. There's a sort of folklore image of slaves traveling at night under the cover of darkness, navigating by the North Star. Allegedly, the song "Follow The Drinkin' Gourd" was a slave song that contained coded instructions for navigating along the Underground Railroad by landmarks along the trail and by using Merak and Dubhe in Ursa Major to identify Polaris...I'm pretty sure this is 20th century embellishment to the story but it's a prominent visual, kind of like Johnny Appleseed's pot hat.

This bit of history is taught so widely in American schools that the term "underground railroad" has just become our word for a secret, grassroots network of routes, safe houses and guides for transporting refugees out of danger.

Here you go. She was a pretty amazing person. If you're from the US and didn't learn about her in school, your school failed you.