Colosseum

The most iconic of the places to visit in Rome, the Colosseum was originally known as the Flavian Amphiteather, and it was commissioned by Emperor Vespasian. It was inaugurated in 80 AD, and could host up to 50000 persons, while its underground area had cages where animals (which would fight against the gladiators) were kept. At the inaugural games in 80 AD, over 9000 wild animals were killed. The name Colosseum was introduced in the medieval times to refer to the Colosso di Nerone, a statue that stood in its vicinity. The Colosseum was abandoned with the fall of the Roman Empire in the 5th Century. It became a fortress occupied by two of the city’s warrior families (Frangipani and Annibaldi) in the Middle Ages. It was eventually depredated of the travertine that originally covered it, and as well as of the marble which was used to build other palaces, among which is the Palazzo Barberini.
Tips: For a global view of the Colosseum, hike the hill on the other side of the road. This is the best angle to take fantastic pictures. Make sure to also catch a glimpse of the Colosseum at night, when it is beautifully illuminated.