Yes, three days is the right length for Rome, and it is what we recommend for a first visit. It gives ancient Rome a full day (Colosseum, Forum, Palatine, plus Monti), the Vatican its own morning followed by Castel Sant'Angelo, and a dedicated day for the piazza core: Pantheon, Trevi, Navona, the Spanish Steps, and Campo de' Fiori. You eat well in three different neighborhoods, fit both Trastevere and a proper Roman trattoria night, and still move at a pace that lets you sit in a piazza rather than sprint past it. What still gets cut: the Galleria Borghese, Villa Borghese, and Testaccio's food scene, which is exactly what a fourth day adds. This suits first-timers, couples, and anyone routing on to Florence next. Stay in Monti: it walks to the Colosseum, sits on the Cavour metro and near Termini for the Vatican hop, and its wine bars make the best base for the evenings. Pre-book the Colosseum-Forum ticket and the Vatican 8am slot before you fly.