The Colosseum may be the most instantly recognizable landmark in Rome and one of the most familiar landmarks anywhere on the planet. The Colosseum was the site of gladiator fights, athletic events, and was often filled with water so that actual naval battles could be enacted.
St. Peter's Basilica
St. Peter's Basilica is technically located in Vatican City, which is surrounded entirely by Rome. Built in the 16th century, St. Peter's is the largest church in the world, capable of holding a congregation of 60,000 people. The extraordinary dome was designed by none other than Michelangelo and still holds the record as the largest dome in the world with a height of 126 feet and a diameter of 414 feet.
Another Vatican City landmark has the touch of Michelangelo to it. The famous frescoes of Biblical scenes on the ceiling of the Sistine Chapel were accomplished by the great artist while lying on his back. The chapel was built between 1473 and 1484 at the request of Pope Sixtus IV. The ceiling of the Sistine Chapel is definitely one of the most breathtaking sights in the world.
One of the famous Seven Hills of Rome, Campidoglio is easily the most sacred of them. If you're in the mood for some physical exercise, the climb up Campidoglio suits the bill. The steps, designed by Michelangelo are long and sloping. When you make it to the top you'll find the Piazza del Campidoglio, notable for being a perfectly precise square.
Rome is dotted with a vast number of ancient ruins, but the Pantheon is the only ancient building that is still intact. The Pantheon began life as a temple for pagan celebrations and services, and was converted into a church in A.D. 609. The opening on the top of the dome served as the singular source of light for the building. The Pantheon's dome was the largest in the world until it was bested by the dome of the Duomo in Florence, Italy.