Colosseum, Rome

The Colosseum is the world's largest ancient amphitheatre, completed in 80 AD under Emperor Titus. Capable of seating 80,000 spectators, it hosted gladiatorial contests for over 400 years and remains Rome's most recognizable symbol. At 48.5 meters tall, it is taller than the average ancient arena by 15 meters, and seating 25,000 more than typical amphitheatres of its era. Its concrete structure used 100,000 cubic metres of travertine stone, weighing 300,000 tonnes—1.5 times heavier than the Sydney Opera House's total structural mass. Today, 6 million visitors per year explore its ruins, paying €16 per ticket.