Rome has many interesting churches with fine artwork worth a visit. Many churches stay open all day but some close for a few hours in the afternoon. These churches have free entrance but some have museums, cloisters, or archaeological areas with a fee.
When entering a church you're expected to be quiet and respectful. Men should remove hats. Some churches won't let you in wearing shorts or sleeveless tops. Most churches allow photos inside with some restrictions.
San Giovanni Laterano - Cathedral of Rome
San Giovanni, Saint John, is Rome's cathedral and the first church of the popes, from the fourth century until the papacy moved to France in 1309. The pope's residence was in the adjoining Lateran Palace. This is the site of the first Christian church ever built in Rome. The current church is Baroque and has cloisters and a museum that can be visited. Be sure to visit the baptistery next door and the Scala Santa and Sancta Sanctorum across the street.
Saint Peter's Basilica - San Pietro in Vaticano
St. Peter's Basilica, San Pietro in Vaticano, is in Vatican City so technically not in Rome. San Pietro is the current church of the pope and one of the largest and most important Catholic churches in the world. Inside the vast interior, there's lots of marble, bronze, and gold artwork, including Michelangelo's Pieta. You can visit Saint Peter's for free but you'll have to pay to see the adjoining Sistine Chapel, with its famous frescoes by Michelangelo and Botticelli, and the Vatican Museums.
Another of the four papal churches, Santa Maria Maggiore has beautiful 5th-century Biblical mosaics. The marble floor, bell tower, and mosaics on the triumphal arch and in the loggia are medieval. Its spectacular ceiling is said to be decorated with gold Columbus brought back from the new world.
The fourth patriarchal or papal church of Rome is San Paulo Fuori la Mura, Saint Paul Outside the Walls, two kilometers from the San Paolo Gate along via Ostiense. It also holds many art treasures and relics including the chains believed to have been used on Paul when he was under arrest.
The Pantheon, built in the year 118 as the Roman temple of all gods, is the best preserved ancient building in Rome. Its vast dome has a circular opening at the top that lets in the only light. In the seventh century, early Christians turned the Pantheon into a church. Inside are many tombs, some holding the bodies of Italian monarchs.
San Clemente, near the Colosseum, is my favorite because of its layers of archaeological excavations underneath, illustrating Rome's interesting history. The current 12th-century church sits on top of the 4th-century church that was built over ruins of 1st-century Roman buildings and a 2nd-century Mithraic cult chamber. The best way to visit the excavations is on a guided tour.
San Pietro in Vincoli - Saint Peter in Chains
San Pietro in Vincoli, also near the Colosseum, was founded in the fifth century to hold the chains that are believed to be those that held St. Peter captive in Mamertine Prison. According to legend, one set of chains was sent to Constantinople and when it was returned to Rome, the two parts miraculously fused together. The church is also home of the famous statue of Moses by Michelangelo, the center of the work known as the tomb of Julius II.
Basilica di Santa Croce in Gerusalemme, Holy Cross in Jerusalem, is one of Rome's popular pilgrimage churches. Santa Croce is a beautiful Baroque church known for its collection of relics. There's also a replica of the Shroud of Turin, the shrine of a young girl being considered for sainthood, and 15th-century frescoes in the apse. Santa Croce started as a church in the fourth century and still has granite columns from the original church. It's been remodeled several times and the church we see today is from the 18th century remodel.
The monastic and archaeological complex includes gardens set in the Castrense amphitheater. There's also a hotel run by the monks, Domus Sessoriana. Santa Croce is near San Giovanni in Laterano (see above).
Santa Maria in Cosmedin
Santa Maria in Cosmedin, between the river and the Circus Maximus, is the most important Greek church in Rome and has some beautiful Byzantine mosaics. In front you'll see lots of tourists sticking their hands into the Boca Della Verita, mouth of truth, a medieval drain cover sculpted to look like a face. According to medieval legend, if you've been untruthful the mouth will snap shut and cut off your hand. Try it at your own risk!
Santa Maria in Trastevere
Trastevere is the neighborhood across the Tiber River from Rome's historic center. Santa Maria in Trastevere is one of Rome's oldest churches and believed to be the first church in Rome dedicated to the Virgen Mary. It originally dates from the late third to early fourth century but was rebuilt in the twelfth century. The church is famous for a Byzantine mosaic behind the altar and a number of 13th-century mosaics. The piazza has a beautiful octagonal fountain.
Santa Maria Sopra Minerva
Another of Rome's Santa Maria churches, Santa Maria Sopra Minerva by the Pantheon is Rome's only Gothic-style church. It was built in the 13th century over what is believed to have been the Temple of Minerva. There's a good collection of art here, including another Michelangelo, Christ Carrying the Cross, and the tombs of St. Catherine, Fra Angelico, and the 16th century Medici popes. Outside is a Bernini sculpture of an elephant with an obelisk on its back.
Santa Maria del Popolo
Santa Maria del Popolo, in Piazza del Popolo, was one of the first Renaissance churches in Rome. The church features Caravaggio's Martyrdom of St. Peter and Conversion of St. Paul. In the Chigi Chapel, created by Raphael, are ceiling mosaics and pyramid-like tombs as well as statues by Bernini.