"The United States Capitol rotunda is the central rotunda of the United States Capitol in Washington, D.C., built 1818–1824. It is located below the Capitol dome, built 1857–1866; the later construction also extended the height of the rotunda walls. It is the tallest part of the Capitol and has been described as its "symbolic and physical heart."
The rotunda is connected by corridors leading south to the House of Representatives and north to the Senate chambers. To the immediate south is the semi-circular National Statuary Hall, which was the House of Representatives chamber until 1857. To the northeast is the Old Senate Chamber, used by the Senate until 1859 and by the Supreme Court until 1935.
The rotunda is 96 feet (29 m) in diameter, rises 48 feet (15 m) to the top of its original walls and 180 feet 3 inches (54.94 m) to the canopy of the dome, and is visited by thousands of people each day. It is also used for ceremonial events authorized by concurrent resolution, including the lying in state of honored dead... The rotunda was designed in the neoclassical style and was intended to evoke the design of the Pantheon (a circular temple in Rome dedicated to all the gods.)." .. https://en.wikipedia.org/wiki/United_States_Capitol_rotunda