The Roman Colosseum has not always been called “the Colosseum” as this modern name only dates back to the Middle Ages. Its proper name is “Amphitheatrum Flavium” or Flavian’s Amphitheater; in fact, you can still see the original name written on the Colosseum today. The Flavian Amphitheater was named after the Flavian Dynasty, the emperors who commissioned its construction.

Source: Art Trav