Set along the Appian Way (Via Appia Antica), the Catacombs of St. Callixtus cover more than 12 miles (20 kilometers), making them Rome’s largest. The remains of martyrs, popes, and an estimated 500,000 Christians were entombed in its 3rd-century tunnels and burial chambers. Tours cover a small portion of the complex, including the Crypt of the Nine Popes, Crypt of St. Cecilia, and two underground basilicas decorated with early Christian symbols.

In any Rome catacombs comparison, St. Sebastian comes out near the top both for its historic heft and artistic treasures. The oldest subterranean Christian burial site in Rome, the Catacombs of St. Sebastian were built in the 2nd century and are where the term “catacomb” was coined. You can only enter with an official guided tour on Tuesdays through Sundays though, and the itinerary covers well-preserved mausoleums, fragments of ancient frescoes, stucco work, and the tomb of St. Sebastian.

Art history buffs can take the guesswork out of choosing Roman catacombs by heading straight to the Catacombs of Priscilla, home to what is considered the oldest surviving rendering of the Virgin Mary. Set in a Roman quarry beneath the convent of the Benedictine Sisters of Priscilla, this burial site covers 8 miles (13 kilometers) of chambers and tunnels, many of which are decorated in early Christian frescoes.

No Rome catacombs travel guide would be complete without a mention of the Catacombs of Domitilla, a favorite among fans of art history for its rare 2nd-century Christian frescoes. The headliner here is the ancient depiction of the Last Supper, but this underground cemetery that covers 10.5 miles (17 kilometers) also holds the Basilica of the Saints Nereus and Achilleus, plus four levels of tunnels where thousands of Christians were laid to rest.

When St. Agnes was martyred at just 12 years of age, her family buried her in their hypogeum, an underground burial chamber common in ancient Rome. Over the subsequent centuries, a catacomb complex grew from this initial tomb and is now a singular example of the evolution from Roman to Christian burials in one site. You can experience this unique site with a guided tour only, so be sure to book in advance.

One of Rome’s lesser-known catacombs began as a 1st-century Roman cemetery. These burial grounds beneath the Basilica of St. San Pancrazio on Janiculum Hill (Gianicolo) are a welcome respite from the crowds in central Rome. Descend beneath the church floor to take in the original architectural details and frescoed burial chamber known as the Cubicle of Botrys, with its rare inscription in Greek identifying the deceased as Christian.

Most tourists overlook the Catacombs of St. Marcellinus and St. Peter, but this underground burial site dating from around the 4th century is one of the most significant in Rome. Dedicated to two Christian martyrs, the complex covers four levels and houses the remains of an estimated 15,000 Christians. The main draw, however, is its artwork. Frescoes decorate many of the underground chambers and depict everything from banquet scenes to Bible stories.

Here’s a catacombs in Rome visitor tip: Seek out sites that aren’t typically open to the public. The Praetextatus Catacombs, home of the exquisitely carved sarcophagus of Emperor Balbinus, are located along the Appian Way near those of St. Callixtus and St. Sebastian. The latter are open to the public, but visitors must make a special request in advance to gain access to the Museums and Catacombs of Praetextatus.

The small size of the St. Thecla Catacombs belies this burial site’s artistic and archaeological importance. Comprising just 22 chambers set along three passageways, this underground complex is decorated in colorful frescoes, including the oldest known depiction of the apostles John, Peter, and Andrew. As in the case of the Catacombs of Praetextatus, a tour of the St. Thecla Catacombs must be requested in advance since the site does not have public visiting hours.