Today, Fort Totten might be best-known as a Metro stop, but during the Civil War, it guarded the nation’s capital. Here, Union soldiers man a Parrott gun at Fort Totten. (Library of Congress)

Did you ever go sledding at Battery Kemble Park? Ice skate at Fort Dupont Park? Play with friends at Fort Lincoln Park? Hike the trail that passes through Fort Marcy Park? Watch the fireworks from Fort Reno Park?

If so, you’ve played where history was made. Union soldiers kept watch for Confederate invaders from all these places — and more — 150 years ago.

By the time the Civil War ended, a circle of forts protected the capital city. But at the start of the war, its only defense was Fort Washington, 12 miles downriver in Prince George’s County. That fort had been built decades earlier to prevent foreign ships from sailing up the river to attack Washington. It couldn’t protect against attacks from Confederate Virginia.

The first new forts guarded the Potomac River bridges and were built as soon as the Union Army marched into Virginia in May 1861. But after the First Battle of Bull Run, when people feared that the Confederates would attack Washington, work quickly began on a series of forts to protect the city and its water supply.

What did they look like? They were earthworks, built mostly of dirt plus some logs. Their high walls were 12 to 18 feet thick.

Who built them? Newly arrived soldiers, hired laborers and contrabands — blacks who had fled slavery.

Where were they built? On high land overlooking the Potomac and Anacostia rivers or routes leading to Washington. Fort Totten, for example, kept watch over a main road into the city from slaveholding Maryland as well as the country home where Lincoln went to escape the city’s heat. And in Alexandria, Fort Ellsworth guarded the railroad, a turnpike and another road Confederate armies could use to come north.

Enemy soldiers would have had a hard time storming any of these forts. After crossing about two miles of cleared land, they would reach a barrier of fallen trees with sharpened branches facing them. If they got through that, they would come to the moat surrounding the fort. And all this time, Union soldiers would be firing rifles and cannons at them. But people in Washington lived in fear of a Confederate attack anyway. The one time Confederates did approach, in an 1864 raid, they were turned back by cannon and rifle fire from the city’s forts.

Want to see where the raiders were stopped? Visit what’s left of Fort Stevens, in Northwest Washington. A small part of the fort’s original area has been preserved and restored. Want to find out what life was like for soldiers defending the capital city? Alexandria’s Fort Ward Museum and Historic Site is the place to go. You can walk around inside the fort’s rebuilt earthen walls, and you might even find a blue-clad “soldier” to answer your questions.

— Carolyn Reeder

Reeder is giving readers a kid’s-eye view of the Civil War. Her books include “Shades of Gray” and “Captain Kate.”