Here a couple of suggestions. I have put together for those who have a limited time in Rome and want to see as much they can on a guided tour!

Option 1

Vatican museums (Sixtine Chapel) | St. Peter’s basilica | Pantheon | Trevi Fountain | Colosseum | Forum

Option 2

Trevi Fountain | Colonna Square | Pantheon | St. Louis Church and Caravaggio Paintings (closed on Thursdays) | Ghetto | Teatro di Marcello | Capitol Square | Forum | Colosseum