After Virginia seceded from the Union on April 17, 1861, the District of Columbia stood on the dangerous border between the divided states. Because of the city’s importance, the Union Army immediately occupied Northern Virginia, allowing troops to protect the city’s bridges and the Aqueduct, its primary water source. After Alexandria was seized in May 1861, construction began on Forts Corcoran, Haggerty, Bennett, Runyon, and Ellsworth around the city. Following the Confederate victory at the Battle of Manassas in July 1861, fears for the safety of the District of Columbia and Alexandria led to plans for a complete fortification system for Washington. Major General George B. McClellan placed Major John Gross Barnard of the Corps of Engineers in charge of the work, and by the end of 1861 Barnard, his engineers, soldiers, and civilians had completed 48 forts surrounding the city. As the war continued, additional forts were recommended to close gaps in the defenses, and the construction of Forts Whipple, Berry, C.F. Smith, and the redoubts to Fort Lyon added needed strength to the capital’s protection. By the end of 1863, 60 forts and 93 batteries defended the city. At the end of the war in 1865, 68 forts surrounded the District of Columbia, linked by batteries, rifle pits, blockhouses, and military roads. On June 23, 1865, orders from Department of Washington Headquarters directed that all but 17 forts, redoubts, and batteries be dismantled, and all the forts were ultimately taken down and the land returned to its prior owners.