As the Civil War loomed, Union forces hurried to protect Washington, DC, which in 1861 was vulnerable if Confederate ships sailed up the Potomac River. Within two years, a protective ring of more than 60 forts rose around the city. Fort Foote, built here on Rozier's Bluff in eight months, became the southernmost defensive site. Its distinction was its advanced coastal artillery, though its modern cannons were never tested in battle. The Union also constructed 93 gun batteries, 20 miles of rifle pits, and 32 miles of military roads around the capital.