Four days is the sweet spot for a first visit to Rome, turning a sightseeing sprint into an actual holiday. Days one to three cover the essentials: ancient Rome (Colosseum, Forum, Palatine), the Vatican with Castel Sant'Angelo, and the piazza core of Pantheon, Trevi, and Navona, each done without rushing. Day four is the release valve, built around the Galleria Borghese, which must be pre-booked on a strict timed slot and cannot be entered without one, followed by the gardens of Villa Borghese and a long, greedy food afternoon through Trastevere or Testaccio. This length suits travelers who hate the forced march, couples, and anyone whose flights bookend the trip awkwardly. For four days we recommend basing in Trastevere: you have accepted a slower pace, and its lanes and trattorias make coming home each night the best part of the day. Beyond four days, add a Tivoli day trip for Hadrian's Villa, or run on to Florence by fast train in an hour and a half. Book the Colosseum, Vatican, and especially the Borghese well ahead.