Today’s Wonder of the Day was inspired by Ethan from GA. Ethan Wonders, “What was the underground railroad” Thanks for WONDERing with us, Ethan!

What do you think about when you hear the word "railroad"? Engines? A line of boxcars? The conductor or the caboose? Tracks stretching off into the distance?

What about an underground railroad? Some of you may think of the subway.

Would you believe the most famous and important Underground Railroad of all time, though, was not made up of engines, boxcars, or track? It might surprise you to learn it was made of…people.

From the earliest moments of American history, boats full of African families were brought to this “land of freedom," not as free men and women, but as slaves to work the land. As soon as they arrived, some began to seek freedom, but escape from the bonds of slavery would not be easy.

People who opposed slavery (called "abolitionists"), along with a large number of other brave men and women, began to create an informal system of secret routes, meeting points, and safe houses to help slaves escape to states that prohibited slavery or even further north to Canada. This informal network of secret routes and safe houses became known as the Underground Railroad.

Since it was not really a “railroad" and it certainly wasn't “underground," how did this name come about? The movement was “underground" in the sense that escaping slaves and those who helped them had to stay out of sight and conceal their actions because they were technically breaking the law.

The “railroad" part of the name came from the words and labels used to describe those involved and their journeys. Runaway slaves would rest, sleep and eat at places given the code names “stations" and “depots." “Conductors" would hide runaway slaves in their homes and teach them secret codes to help them find the next “station" along the route.

The Underground Railroad consisted of a vast network of people and was not run by any single organization or person. Indeed, most of those involved only knew about their particular part of the operation and not the overall picture.

The Underground Railroad effectively moved many slaves to freedom each year. Its use peaked between 1850 and 1860. Some estimate that up to 100,000 slaves had escaped via the Underground Railroad by 1850.

For all those involved, running away to freedom was a dangerous and difficult ordeal. Slaves had to first escape from their slaveholders.

Sometimes a "conductor" would pose as a slave, enter a plantation, and then guide runaways northward. Most of the time, though, slaves had only themselves to rely on to plan and execute their escape.

Runaways would move at night, traveling 10 to 20 miles to the next “station." During the day, they would rest and eat, hiding out in all sorts of places.

The journey was long and stressful. The length of the route to freedom varied but often exceeded 500 to 600 miles.

Runaway slaves who were strong — and lucky — might make it to freedom in as little as two months. For the weak and unlucky, the journey could last more than a year.

Harriet Tubman was one of the most famous “conductors" along the Underground Railroad. Born into slavery in Maryland, she planned her escape when she learned she was going to be separated from her family and sold.

With the help of others, she made her way to Philadelphia, starting out in the back of a wagon covered with a sack. She later described freedom as "heaven."

In Philadelphia, Harriet worked hard to save money to rescue her family. She eventually helped more than 300 slaves reach freedom.

Harriet became known as "Moses" because she returned 19 times to the South (or "Egypt") to help runaway slaves use the Underground Railroad to gain freedom. She became known for using music, Bible verses, and folklore to alert escaped slaves to danger and give them directions to safe houses.

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