The Rotunda lies under the great dome at the center of the Capitol. It is 96 feet in diameter with a floor area of about 7,000 square feet. It is almost twice as high as it is wide and encloses more than a million cubic feet of space. The original Rotunda was designed by Charles Bulfinch, who completed it in 1824. He divided the Virginia sandstone walls into compartments framed by Doric pilaster and decorated the upper walls with sculptural enrichments. The floor was paved with stone from Seneca, Maryland. Originally the room was lit by a single oculus at the crown of the inner dome.
In 1855 the inner dome was removed to make way for the new cast-iron dome that Thomas U. Walter added in the 1850s and 1860s. It raised the room's height from 96 feet to 186 feet, provided 36 windows for light and ventilation, and gave the space a greater sense of grandeur and magnificence. Architecturally, today's Rotunda is an eclectic mix of Grecian, neoclassical and baroque styles.