2 days — The sprint
Day 1: Colosseum + Forum + Palatine (morning), Pantheon + Piazza Navona + Trevi (afternoon). Day 2: Vatican Museums + Sistine Chapel + St Peter's (morning), Trastevere (evening). It's exhausting but covers the essentials.
3 days — The sweet spot
Add: Borghese Gallery (book ahead!), Spanish Steps, Monti neighbourhood, gelato tour. Three days lets you breathe between the big sites and discover quieter corners.
4 days — Comfortable
Add: Appian Way cycling, Testaccio food market, Castel Sant'Angelo, a cooking class or food tour. Four days means no rushing and time for long lunches.
5+ days — In-depth
Add: day trip to Tivoli (Hadrian's Villa + Villa d'Este), Ostia Antica, Jewish Ghetto deep dive, Capitoline Museums, a neighbourhood-by-neighbourhood exploration. Rome rewards extra days more than almost any city.
Our recommendation: 3 days minimum, 4-5 ideal
Book Vatican + Colosseum + Borghese on day 1 of planning — these three sell out.