Potomac River to be the site of the "President's House" (later called the "Executive Mansion", now the White House) and the "Congress House" (now the United States Capitol). Custis located the building on a prominent hill overlooking the Georgetown-Alexandria Turnpike (at the approximate location of the present Eisenhower Drive in Arlington National Cemetery), the Potomac River and the growing Washington City on the opposite side of the river. The mansion was built using materials on site, though the building was interrupted by the War of 1812 (and material shortages after the British burned the American capital city). The Custis mansion's exterior was completed in 1818. The north and south wings were completed in 1804. The large center section and the portico, presenting an imposing front 140 ft (43 m) long, were finished 13 years later. The house has two kitchens, a summer and a winter. The most prominent features of the house are the 8 massive columns of the portico, each 5 feet (1.5 m) in diameter. Guests at the house included such notable people as Gilbert du Motier, Marquis de Lafayette, who visited in 1824 (see: Visit of the Marquis de Lafayette to the United States). At Arlington, Custis experimented with new methods of animal husbandry and other agriculture. The property also included Arlington Spring, a picnic ground on the banks of the Potomac that Custis originally built for private use but later opened to the public, eventually operating it as a commercial enterprise. Custis married Mary Lee Fitzhugh. Their only child to survive to adulthood was Mary Anna Randolph Custis. Robert E. Lee, whose mother was a cousin of Mrs. Custis, frequently visited Arlington and knew Mary Anna as they grew up. Two years after graduating from West Point, Lieutenant Lee married Mary Anna Custis at Arlington on June 30, 1831. For 30 years Arlington House was home to the Lees. They spent much of their married life traveling between United States Army duty stations and Arlington, where six of their seven children were born. They shared this home with Mary's parents. After their deaths, Mary's parents were buried not far from the house on land that is now part of Arlington National Cemetery. The Custis family extensively developed the Arlington estate. Much of the steep slope to the east of the house became a cultivated English landscape park, while a large flower garden with an arbor was