Arlington House (formerly the Custis-Lee Mansion) was the home of Robert E. Lee and his family for thirty years and is uniquely associated with the Washington and Custis families. George Washington Parke Custis, Lee’s father-in-law, built the house between 1802 and 1818 to be his home as well as a memorial to George Washington, his step-grandfather. Lee made his historic decision to resign from the US Army at Arlington House and wrote his resignation letter in his second floor bedchamber.

Lee was distressed when news reached him that Virginia had adopted an Ordinance of Secession on April 17, 1861. He had supported preservation of the Union that his father and uncles had helped create and opposed slavery, but he remained loyal to his native state. He was at home at Arlington on April 20, 1861, when he made his decision to resign his commission in the U.S. Army. Two days later Lee left Arlington for Richmond to accept command of Virginia's military forces with the General Assembly's approval; he never returned to Arlington. About a month later, with Union occupation imminent, Mrs. Lee also left Arlington, managing to send some of the family valuables off to safety. After Arlington became headquarters for the officers who were superintending the nearby defenses of Washington, many of the remaining family possessions were moved to the Patent Office for safekeeping. Some items, however, including a few of the Mount Vernon heirlooms, had already been looted and scattered.

A wartime law required that property owners in areas occupied by Federal troops appear in person to pay their taxes. Unable to comply with this rule. Mrs. Lee saw her estate confiscated in 1864. An 81 hectare (200 acre) section was set aside as a military cemetery, the beginning of today's Arlington National Cemetery. In 1892 George Washington Custis Lee's suit against the Federal Government for the return of his property was successful. By then, hundreds of graves covered the hills of Arlington and he accepted the Government's offer of $150,000 for the property.

Arlington National Cemetery was established by Brigadier General Montgomery C. Meigs, who commanded the garrison at Arlington House, appropriated the grounds June 15, 1864, for use as a military cemetery. His intention was to render the house uninhabitable should the Lee family ever attempt to return. A stone and masonry burial vault in the rose garden, 20 feet wide and 10 feet deep, and containing the remains of 1,800 Bull Run casualties, was among the first monuments to Union dead erected under Meigs' orders. Meigs himself was later buried within 100 yards of Arlington House with his wife, father and son; the final statement to his original order. For some years the superintendent of the cemetery and the staff used the mansion as offices and living quarters. Beginning in 1925, the War Department began restoring the house, and in 1933 it was transferred to the National Park Service. In 1955 the mansion was designated as a memorial to Robert E. Lee. Over the years some of the original furnishings have been obtained. The hope is to restore the house to its pre- Civil War appearance and to recreate the home that Lee and his family loved so much.

http://en.wikipedia.org/wiki/Custis-Lee_Mansion