The Tomb of the Unknowns is part of the Arlington Memorial Amphitheater. The Memorial Amphitheater has hosted state funerals and Memorial Day and Veterans Day ceremonies. Ceremonies are also held for Easter. About 5,000 people attend these holiday ceremonies each year. The structure is mostly built of Imperial Danby marble from Vermont. The Memorial Display room, between the amphitheater and the Tomb of the Unknowns, uses Botticino stone, imported from Italy. The amphitheater was the result of a campaign by Ivory Kimball to construct a place to honor America's soldiers. Congress authorized the structure March 4, 1913. Woodrow Wilson laid the cornerstone for the building on October 15, 1915. The cornerstone contained 15 items including a Bible and a copy of the Constitution.