A dome is a rounded roof or ceiling shaped like the top half of a sphere, like an upside-down bowl. The ancient Romans pioneered dome construction, and the Pantheon in Rome, completed nearly 2,000 years ago, still has the world's largest unreinforced concrete dome. When you stand beneath a great dome, you feel the space open up above you in a way flat ceilings can't match.

Domes appear on important buildings worldwide: the United States Capitol, St. Peter's Basilica in Vatican City, and countless mosques and temples. Architects love domes because they're both beautiful and structurally strong, distributing weight evenly around their base. Some modern stadiums use domes (often called domed stadiums) to keep out the weather while covering huge spaces without interior pillars blocking views.

The word also describes anything dome-shaped. A geodesic dome is a special rounded structure made of triangular pieces, popularized by architect Buckminster Fuller. Scientists sometimes call the top of someone's head a dome, and mountain peaks can be described as domes when they're smoothly rounded rather than jagged.