in Classical and Neoclassical architecture, building or room within a building that is circular or oval in plan and covered with a dome. The ancestor of the rotunda was the tholus (tholos) of ancient Greece, which was also circular but was usually shaped like a beehive above.

An example of a Classical Roman rotunda is the Pantheon erected at Rome about AD 124. The Villa Rotonda (Capra) at Vicenza is an Italian Renaissance example, designed by the influential architect Andrea Palladio. Begun in 1550, the building features a large central hall that is circular and has a low dome. It was later copied by English architects in such manor houses as Chiswick House, begun in 1725 in London. In the gardens of Chiswick House is a rotunda that serves as a gazebo, or pavilion. The central hall of the U.S. Capitol in Washington, D.C., and the rotunda of the General Grant National Memorial (Grant's Tomb) in New York City are examples of the rotunda in its familiar role as part of a monumental public building.

Sometimes the term rotunda is also used in reference to the dome itself, whether or not the area beneath it is a single oval or circular room. In this sense, the dome of St. Paul's Cathedral in London is a rotunda.