What supports the floor of the Rotunda?

The correct answer is that the floor of the Rotunda is supported by the Crypt. The Crypt is an underground chamber directly beneath the Rotunda that serves as a vital support structure. It was originally intended to be the burial place for George Washington, but he was never interred there. The space functions architecturally by providing stability to the heavy, elaborate structure of the Rotunda above it.

Understanding this relationship highlights the sophisticated engineering behind the Capitol building, demonstrating how historical design elements were achieved. The foundation of the Capitol certainly plays an essential role in the overall stability of the structure, but it is the Crypt specifically that acts as a direct support mechanism for the floor of the Rotunda. The Senate chamber and the dome structure, while integral components of the Capitol, do not provide support for the Rotunda's floor itself.