The National Gallery of Art is an art museum owned and operated by the government of the United States. It consists of two buildings, the East Building and the West Building, connected by an underground passage and both located in the National Mall in Washington, D.C. The National Gallery of Art is affiliated with the Smithsonian Institution, though it is governed under a separate charter. The gallery exhibits one of the finest art collections in the world, exemplifying major accomplishments in painting, decorative arts, sculpture, and works on paper from the Middle Ages to the present. The National Gallery of Art was created by Congress, with funds for construction and a substantial art collection donated by Andrew W. Mellon, in 1937. The museum’s original collection of Italian art was contributed by Samuel H. Kress. The original museum building was designed by architect John Russell Pope. Opening in March 1941, it is now called the West Building. The building is neo-classical with a gigantic, columned portico and a huge dome reminiscent of the Pantheon, except for the West Building's symmetrically attached, extended wings. Opening in 1978, the East Building was designed by noted architect I.M. Pei. The building is also geometrical, but fragmented or faceted by comparison to the West Building's cool classicism. From above, the building seems as if made of interlocking diamonds. In 1999, the National Gallery of Art also opened an adjacent sculpture garden. The West Building features a fine collection of paintings and sculptures by European masters from the medieval period through the late-19th century, as well as works by American artists of the same period. The collections include many paintings by Vermeer, Monet, Van Gogh, Rembrandt, and the only painting by Leonardo Da Vinci within the United States. The East Building concentrates on modern and contemporary art, with a collection which includes works by Picasso, Matisse, Andy Warhol, Jackson Pollock, and Alexander Calder. The East Building also houses the main offices of the National Gallery of Art and a large research facility.