If your time in Rome is limited to one day, this sunrise-to-sunset itinerary is what you need!
Start early in the morning with a visit to the Colosseum. Then take Via Sacra to the Roman Forum and wander through the ancient complex. Move to Venice Square which is located at the intersection of several important Roman boulevards and which boasts an enormous monument to the first king of Italy – Victor Emmanuel II. This white marble altar is one of the largest and tallest buildings in Rome.
Continue to what is probably the most famous fountain in the world - Trevi Fountain. You can see hundreds of tourists throwing coins into the fountain every day since it is said that doing this ensures your return to Rome one day. Next stop is the Pantheon, well-known for its oculus that lets the daylight (but also the rain) in through the top of the dome.
Walk through the prominent Navona Square and finish your tour at St. Peter's Basilica. There might not be time to explore all the Vatican Museums, but make sure you don't miss the Sistine Chapel!