The 2,000-year old Colosseum covers six acres, and could seat over 45,000 spectators. How did the Romans succeed in putting a roof across this enormous amphitheater, some 600 feet in diameter? The concrete structure of the Colosseum has endured largely intact, but the vast canvas awning shown in ancient pictures has long since disappeared.

Two theories of how the spectators at the Colosseum were protected from the fierce Mediterranean sun were tested on a 15th-century bullring in a city called Barcarrota, in an area controlled by the Romans 20 centuries ago. In one experiment, sails were attached to horizontal masts around the perimeter of the ring and furled out over the seats. In the other experiment, perpendicular masts supported a network of miles of ropes on which the sales were hung.

Is this how the Romans did it? Two experts, engineer and long-time sailor Owain Roberts, and classicist Norma Goldman responded to selected questions during a live event, and to additional questions e-mailed to this Web site for one week thereafter. Check out the archived questions and answers.