Papal Basilica of Saint Mary Major

Built in the mid-5th century following a legendary summer snowfall that marked out its site, Santa Maria Maggiore preserves some of the oldest surviving Christian mosaics in Rome inside a mostly Baroque exterior. It's one of only four papal basilicas — alongside St. Peter's, St. John Lateran, and St. Paul Outside the Walls — and holds relics along with the tomb of Pope Francis. Its location near Termini station makes it an easy stop even on a tight itinerary, and it draws steadier crowds than the outer basilicas without ever matching St. Peter's. It suits anyone interested in early Christian art as much as pilgrims.