the ColosseumCol·os·se·um, the /ˌkɒləˈsiːəm $ ˌkɑːl-/ (also the Coliseum) an amphitheatre (=large circular theatre without a roof) in Rome which was built during the first century AD and is now one of the most famous ancient Roman buildings. It is thought of especially as a place where fights involving gladiators and wild animals were organized as a form of entertainment.