The Basilica of the National Shrine of the Immaculate Conception is a prominent Latin Rite Catholic basilica located in Washington, D.C., honoring the Blessed Virgin Mary as Our Lady of the Immaculate Conception, the Patroness of the United States. It is the largest Catholic church in the United States, the eighth largest religious structure in the World, and the tallest building in Washington, D.C. An estimated one million pilgrims from around the country and the world visit the basilica each year. The basilica is located on Michigan Avenue in the northeast quadrant of Washington, on land donated by The Catholic University of America.
Construction of this church, notable for its Neo-Byzantine architecture, began in 1920 under Philadelphia contractor John McShain and opened unfinished in 1959. The Basilica is the Patronal Catholic Church of the United States, honoring Mary, Mother of God, under the title Immaculate Conception. It is not the cathedral church of the Archdiocese of Washington; the Cathedral of St. Matthew the Apostle serves as church of the Archdiocese. The Basilica is sometimes confused with the Washington National Cathedral.
The Basilica does not have its own parish community, but it serves the adjacent University, the United States Conference of Catholic Bishops (located down the street), and hosts numerous Masses for organizations of the Church from across the United States.
The Basilica houses 70 chapels honoring Mary and reflecting the origins of the Catholic immigrants and religious orders whose generosity erected them. Its Greek-styled interior is crowned with numerous domes decorated in mosaics, similar to the Basilica of St. Mark in Venice, Italy, but much larger. The mosaics feature American renditions of traditional Catholic images. Artist Jan Henryk De Rosen, who presided over the shrine's iconography committee was also responsible for much of its decor, including composing the large mosaic over the northern apse.
The exterior of the Basilica is 459 ft (140 m) long, 240 ft (73 m) wide, and 237 ft (72 m) tall to the top of the cross on the dome. The diameter of the main (Trinity) dome of the Basilica is only 7 feet (2.1 m) smaller than that of the dome of the United States Capitol. The shrine was built in the style of medieval churches, relying on masonry walls and columns in place of structural steel and reinforced concrete. It was designed to seat over 2,000 worshipers and includes modern amenities such as a basement cafeteria, hidden public address speakers to carry speech at the altar to the rear of the building, air conditioning and the largest (in 1959) radiant heating slab in the world.