The Colosseum had a retractable roof, operated by a crew of sailors, almost 2000 years before any modern stadium. It was called the velarium: an enormous awning of canvas and rope that could be drawn across the open top of the arena to shade fifty thousand spectators from the Roman sun. It was so large and so complex that ordinary labourers could not manage it. The Romans brought in sailors from the imperial fleet, men who spent their lives handling rigging and sail, and stationed them at the top of the structure to extend and retract the canvas as the day moved. A building that has stood, roofless to our eyes, for centuries was in fact designed to be covered. That is the pattern with the Colosseum: almost everything about it was way more advanced than it looks today... Construction began around 72 AD under the emperor Vespasian. Once completed, it was the largest amphitheater in the Roman world: an elliptical structure of stone, concrete, and travertine, 189 meters long, rising as high as a modern fifteen story building. It could hold around 50,000 people and the staircases allowed that entire crowd to enter and leave with a speed that modern stadium designers still study. Beneath the arena floor lay the hypogeum, a hidden labyrinth of tunnels, cells, and machinery. Animals and gladiators waited there in the dark. Numerous trap doors opened in the wooden floor above them, and through hidden lifts and ramps a lion, a leopard, or an armed man could rise into the daylight as if from nowhere, in front of tens of thousands of people. The Romans knew that they had built something that would outlast them so completely that the Colosseum became, for the people who came after, a measure of the world's own endurance. In the 8th century, an epigram attributed to the Venerable Bede offered a prophecy that has never lost its allure: "As long as the Colosseum stands, so shall Rome; when the Colosseum falls, Rome shall fall; when Rome falls, so falls the world." If you enjoyed this, I write a weekly newsletter read by over 50,000 people who love rediscovering the beauty of the past. You can join us here: If you'd like to support my work, a paid subscription is what makes it possible.