The Colosseum is a monumental feat of Roman engineering, completed in 80 AD under emperors Vespasian and Titus. This elliptical structure, 189 metres long by 156 metres wide and reaching 48 metres high, is a freestanding wonder unlike theatres carved into hillsides. Its key innovation lies in extensive use of opus caementicium, a Roman concrete, allowing for the construction of radiating vaults that functioned as building blocks for tiered seating. A network of lighter barrel vaults supported the steeper, wedge-shaped seating tiers, this ingenious design providing excellent sightlines and distributing weight efficiently. Further enhancing structural integrity, the outer wall employs a post-and-lintel system with alternating sections of piers and columns supporting horizontal beams for a skeletal framework. The arena floor, sloped slightly inwards, channelled rainwater through a network of channels and drains beneath the wooden floor, eventually emptying it into a complex subterranean network. These technical advancements, along with meticulous detailing, ensured the Colosseum's longevity as a stage for Roman entertainment for centuries. It staged elaborate spectacles such as gladiatorial combat, animal hunts (venatio), and even sea battles (naumachiae). These events, particularly the venatio, resulted in the slaughter of countless wild animals imported from across the empire, contributing to the extinction of some species. The Colosseum appears on both the list of Seven Wonders of the Middles Ages, and that of the New Seven Wonders of the World.