The Colosseum or Coliseum, also known as the Flavian Amphitheatre, is an oval amphitheater in the center of the city of Rome, Italy. Built of concrete and sand, it is the largest amphitheater ever built and is considered one of the greatest works of architecture and engineering ever. Started by Emperor Vespasian of the Flavia family, it was opened by his son Titus in 80 A.D. What we see nowadays is just the skeleton of what was the greatest arena in the ancient world. There is now a museum dedicated to Eros located in the upper floor of the outer wall of the building. Part of the arena floor has been re-floored. Beneath the Colosseum, a network of subterranean passageways once used to transport wild animals and gladiators to the arena opened to the public in summer 2010.