Arlington National Cemetery, across the Potomac from Washington in Arlington, Virginia, is the United States’ principal military cemetery, covering 639 acres and holding more than 400,000 burials while remaining active. The site began as Arlington Plantation, where George Washington Parke Custis built Arlington House and where Robert E. Lee later lived through his marriage to Mary Anna Randolph Custis. Union forces occupied the estate in 1861, and it became a military cemetery in 1864 amid wartime need and the political significance of denying Lee’s return. The property later figured in a Supreme Court case, included Freedman’s Village, ended segregated burials in 1948, and evolved into a major national memorial landscape.