Complex sentence: The inaugural games of the Flavian Amphitheatre were held in AD 80, on the orders of the Roman Emperor Titus, to celebrate the completion of the Colosseum, then known as the Flavian Amphitheatre (Latin: "Amphitheatrum Flavium").
Split into simpler sentences: The inaugural games of the Flavian Amphitheatre took place in Rome in 80 AD by proclamation of the Roman Emperor Titus. The games were instituted to celebrate the completion of the Colosseum, then known as the Flavian Amphitheatre (Latin, "Amphitheatrum Flavium").