Colosseum

"Ancient Romans attended many spectacles in this massive amphitheatre. The audience kept cool thanks to a billowing canopy that protected them from the blazing sun. Without modern materials how did the Roman builders complete the task of covering the Colosseum? NOVA tries out two concepts: one, a traditional theory, holds that a giant spider web of ropes secured reams of cloth covering. The other, a new hypothesis, borrows from the elegant mast and boom construction that was used to unfurl the canvas sails of ancient ships."