In April of 1917, construction of the Rome-Cassino railroad line just outside the gates of the Porta Maggiore on the Via Praenestina in Rome was halted by a cave-in. The cause turned out to be the collapse of an ancient roof of a building nobody knew was under their feet. As it happens, most ancient Romans probably had no idea it was under their feet either. It was deliberately built about seven or eight meters (23-26 feet) below the level of the ancient Via Praenestina in the early decades of the 1st century A.D. and constructed in such a way as to give little indication that something was going on down there.
The part that caved in was the barrel vaulted roof of a dromos, a long entrance gallery that sloped down from the surface and then turned at a right angle for a short passageway into a small square atrium topped by a domed vault. Light was provided by a skylight at the beginning of the dromos, another where it corners into the short passageway and a third in the atrium vault. The atrium opens into a rectangular hall 12 meters (40 feet) long and nine meters (30 feet) wide divided into three barrel-vaulted sections. Two rows of three square pillars separate the central nave from the aisles on either side. The nave is wider than the aisles and opens into a semi-circular apse at the bottom. The main hall was lit by chandeliers and lamps.
This is the classic basilica design, used by the Romans as loci for business transactions, court proceedings and imperial audiences. What makes this building unique in the Roman world is that it is a basilica built for a pre-Christian religious purpose. Roman temples had columned porticos, a main room where the deity’s image was housed and one or more back rooms to store equipment, sacrifices and treasure. When Christianity was decriminalized by the Edict of Milan in 313 A.D., Constantine wanted to build impressive churches, as opposed to the cramped underground chapels, catacombs and private homes used when it was a suppressed religion. He turned to the basilica as a public building of widely-recognized civic importance that was not associated with pagan religious practices, and Christian churches have embraced that ancient design ever since.
The Porta Maggiore basilica is not a temple and it’s not Christian, but it’s definitely a religious building. The decoration attests to that, as does the fact that it was built underground in the first place. Above a wainscoting-like band of red paint of which there are sections extant, the walls and vaults are covered with exquisite white stucco reliefs of mythological scenes like Sappho’s legendary suicide by throwing herself off the Leucadian cliff into the ocean, Zeus’ eagle abducting Ganymede, Medea offering a magical narcotic beverage to knock out the dragon guarding the Golden Fleece, Orpheus leading Eurydice back from the underworld, Hercules rescuing Hesione from the sea monster, Paris and Helen, Hippolytus and Phaedra, the centaur Chiron teaching Achilles, and one of the Dioscuri kidnapping one of the Leucippides for his bride. There are also heads of Medusa, children at play, animals, plants, a wedding, winged Victories, Nereids, bacchantes, herms, urns, a pygmy returning to his hut after a successful hunt, a table groaning with food and drink, stylized landscapes with garlanded columns and votive trees, worshippers praying to or decorating altars, ritual devotions, and all kinds of geometric and floral flourishes. The quality of the reliefs is exceptionally high and the consistency of style confirms a first century A.D. date.
The method of construction is one of the most fascinating aspects of this unique structure. Nothing else like it has been found. Builders dug seven or eight meters down into the soft volcanic tufa creating trenches where the perimeter walls would go and squared pits where the pillars would go. They then poured that fabulous Roman concrete into pits and let it set. No need for forms or scaffolding; the tufa itself provided the support necessary. Once the concrete had hardened, they poured the concrete for the arches over the pillars and the barrel vaulted ceilings. Lastly they dug out all the tufa from the interior and voila: underground basilica. So damn ingenious. Even though the walls were painted and stuccoed, you can still see the rough texture imprinted on them by the tufa as they dried.
The mosaic floors have remained essentially intact. Made primarily of white tiles with black borders around the walls and pillars, there are untiled areas whose outlines suggest they were once the bases of statues or large urns. In the center of the nave and aisles are small pits that archaeologists believe were the anchor points for the chains used to raise and lower the chandeliers. The skeletal remains of a dog and a pig were found underneath the floor of the apse, likely a sacrifice made during the consecration of the basilica.
Since its discovery, historians have proposed several possible uses for the building — tomb, nymphaeum, site of a funerary cult of the dead — but the prevailing theory at the moment is that it was a place of worship for members of a Neopythagorean mystery religion. Neopythagoreanism was a revival of an earlier school of thought espoused by the mathematician Pythagoras of Theorem fame that held that union with the divine was possible through ascetic living and contemplation of the cosmic order. Metempsychosis, or the transmigration of souls, was a central tenet. The presence of multiple scenes dealing in the movement of souls to and from the underworld (Orpheus, Sappho) and transitions from one state of being to another (Ganymede, the Dioscuro and Leucippid) on the basilica decorations are clues to its possible association with this Hellenistic mystery cult. There is so much variety in the stucco reliefs, however, and so much we don’t know about the symbolism behind them, that the basilica’s usage may remain a mystery forever, which is fitting, really.
This marvelous space was filled with rubble and sealed just a few years after it was built. Its location may explain its fate. The basilica is believed to have been built on property belonging to the Statilius family. This is evidenced by a burial ground nearby for the servants and freedmen of the Statilii. This family was new, only a few generations from its first consul Titus Statilius Taurus I who had fought for both Anthony and Octavian during the Triumvirate and ultimately backed the right horse at the right time leading Octavian’s armies at Actium.
The Statilii were very wealthy (gotta have big money to come from nothing and successfully climb the cursus honorum) and one of them,
Titus Statilius Taurus IV, became a target of imperial greed because of his wealth. Titus Statilius Taurus IV was consul in 44 A.D., proconsul of Africa from 51 to 53 A.D. and the great-uncle of the future empress Statilia Messalina, third wife of Nero. After his return from Africa, he was caught in the cross-hairs of Emperor Claudius’ notorious wife Agrippina.
Tacitus describes the events in his Annals, Book XII, Chapter 59:
Statilius Taurus, whose wealth was famous, and whose gardens aroused [Agrippina's] cupidity, she ruined with an accusation brought by Tarquitius Priscus. He had been the legate of Taurus when he was governing Africa with proconsular powers, and now on their return charged him with a few acts of malversation, but more seriously with addiction to magical superstitions. Without tolerating longer a lying accuser and an unworthy humiliation, Taurus took his own life before the verdict of the senate.
Rubble found in the basilica dates to the middle of the first century, and archaeologists believe it was sealed during the reign of the Emperor Claudius. So we have a brilliantly built, expensively decorated, secret underground basilica constructed on Statilius land just outside the ancient walls of the city. Sounds like something a very rich person with “an addiction to magical superstitions” might build, no? The missing statuary and urns and missing altar could have been confiscated and/or destroyed by imperial order, or they could have been removed by his people before the basilica was sealed to prevent them from getting into any more trouble.
That theory was proposed by French historian Jérôme Carcopino who was Director of the French School in Rome in 1937. More recently, historian and professor of Roman art and archaeology Gilles Sauron proposed that the basilica was constructed by an earlier Statilius, Titus Statilius Taurus III, second son of the original new man Titus Statilius Taurus, who was consul in 11 A.D. Recent conservation work has found different sizes of mosaic tiles and possible indications that some of the stucco reliefs may have been done at different times, so both historians may be right after all.
Once it was rediscovered by the railway workers, the basilica was restored several times. To provide access to the structure which is now 13 meters (about 43 feet) below street level, a staircase was built from the Via Praenestina connecting to the short passageway right before it opens into the atrium. It has very rarely been open to the public, however, because of its delicate condition. Stucco is extremely susceptible to moisture and as early as 1924, just seven years after it was found, water damage became such a concern that conservators covered the top with a cap of pipe-clay to form an impermeable membrane. It proved not to be impermeable, unfortunately, so 25 years later they tried again. In 1951 the railway paid for construction of a dome of reinforced concrete to protect the delicate basilica beneath from the vibrations of the trains and water damage. It was a stop-gap measure and the basilica continued to deteriorate.
Because of its precarious condition, this beautiful basilica, unique in the world, is barely known. That may change now that a new restoration more than 10 years in the making has addressed long-term issues with water penetration, cleaned out the plague of parasitic microorganisms that feast on stucco, and installed eight machines that filter the air to operating-room cleanliness and monitor the temperature and humidity. Work on the dromos, atrium and apse is complete, but it is ongoing on the vaulted ceilings. They’re still raising funds to restore the naves.
The basilica will be open to guided tours only, reservations obligatory (call 0639967700 to book a visit). Because an excess of human bodies with their breathing and sweating and greasiness and germs can drastically alter the precarious environmental balance of the structure, tours are offered on the second and fourth Sunday of the month.
This Italian news story shows the basilica before restoration:
This is a fly-through with some CG effects of the basilica as it is now: