The main feature of the structure consists of an open-air amphitheater, elliptical in plan, with a seating capacity of about 4,000 persons. Its diameter, north and south axis, is 200 feet, and 152 feet on its east and west axis. It has a height of approximately 30 feet. The amphitheater is inclosed by a marble colonnade with entrances at the ends of the principal axis. The main entrance is from the east, and this section contains a reception hall and stage on the main floor, a museum room or “Valhalla” on the second floor, and a chapel in the basement. Under the floor of the colonnade, crypts are provided for the burial of distinguished soldiers, sailors, and marines. The amphitheater, erected at a cost of $825,000 is built of white marble from Vermont. Inscriptions commemorate the great wars of the United States. Immediately to the east of the main entrance is the Tomb of the Unknown Soldier, which was completed by the War Department in accordance with plans that provide also for a great approach to the tomb and the amphitheater. TOMB OF THE UNKNOWN SOLDIER At the time when the rites for the Unknown Soldier were solemnized, on November 11, 1921, the time for preparation was so short that the location of the tomb on the terrace in front of the amphitheater was quickly decided upon. The casket was inclosed in what was designed to be the base of a monument which was to be erected later. The preliminary work was designed by Thomas Hastings, of the firm of Carrere & Hastings, architects of the amphitheater. Five years later, on July 3, 1926, Congress authorized the Secretary of War to secure by competition designs for a monument to cost $50,000, and provided that the accepted design should be subject to the approval of the Arlington Amphitheater Commission (the Secretaries of War and of the Navy), the American Battle Monuments Commission, and the Commission of Fine Arts. A competition was held, in which there were 39 competitors, 5 of whom were selected to enter the final stage. The final award was made to Thomas Hudson Jones, sculptor, and Lorimer Rich, architect, of New York City. The competitors generally based their designs on such a modification of the terrace as would place the monument at the head of a flight of steps, the approaches to which called for rearrangement of the immediate foreground of the terrace. Congress accepted the winning design, and a supplemental appropriation was made for carrying out the design. The work of completing the Tomb of the Unknown Soldier was in charge of the Quartermaster General of the Army. The cost of the memorial, constructed of Colorado Yule marble, was $400,000.