Fort Stevens, now partially restored and located at 13th and Quackenbos Streets, NW, was built to defend the approaches to Washington from the 7th Street Pike (now Georgia Avenue) which was then the main thoroughfare from the north into Washington. Originally called Fort Massachusetts by the soldiers from that state who constructed the fort, it was later named after Brigadier General Isaac Ingalls Stevens, who was killed at the Battle of Chantilly, Virginia, September 1, 1862.

In the summer of 1864, General Ulysses S. Grant had Confederate General Robert E. Lee in a deathtrap around Richmond and Petersburg. When General Grant had moved south, he stripped Washington, D.C. of many well trained troops. As a result in July of 1864 there were only 9,000 troops to defend the city, down from over 23,000 that had been there the year before. Those that were left were primarily poorly trained reserves. General Lee sought desperately to find a way out of his predicament around Petersburg. He decided to send General Jubal A. Early with about 20,000 troops to strike at Washington, which his spies had reported was poorly defended. On June 12, General Early started his march from behind Petersburg, and by July 9, he was at Frederick, Maryland, where he demanded and received $200,000 to spare the city. On the same day, General Early defeated Union General Lew Wallace at the Monocacy River. In the light of later events, General Wallace's defeat after a stubborn fight became a victory for the Union because he was able to delay Early's advance for a day. On July 10, Early encamped at Rockville, Maryland, 10 miles from Fort Stevens.

As a result of the rapid and successful movement of Early, the men of the War Department seemed paralyzed, and would give no orders except as they received them from General Grant. General Grant understood the situation and sent the 25th New York Cavalry, which left City Point, Virginia, on July 7 and reached Fort Stevens midnight of July 10. Also on the 7th, the 1st and 2nd Divisions of the 6th Corps, under General Horatio G. Wright, left City Point. A few hours later General W. H. Emory, with part of the 19th Corps just returning from New Orleans to join Grant, left Fort Monroe for Washington.

By noon of July 11, Confederate General Early came in full view of Fort Stevens, reconnoitered the area and found the fort poorly manned. During the afternoon of that day, General Early tried to find a weak spot in the line, but was met everywhere by fort guns and musketry. Supporting Fort Stevens were the guns from Fort DeRussy on the left and Fort Slocum on the right. When examining the works at daylight on July 12, Early saw the parapets lined with seasoned troops; he then decided to abandon the idea of capturing Washington, but planned to give the Yankees a fight anyway. By nightfall of July 12, the Rebels were sent into full retreat, and the Union Capital had been saved.