Part of the extensive network of tunnels underneath the Baths of Caracalla will open to the public starting December 21st for the first time since their rediscovery in the late 19th century.
Construction on the 11-hectare thermal bath complex probably began under the Emperor Septimus Severus, but it opened in 216 A.D. during the reign of the Emperor Caracalla, hence the name. The baths were free for public use and could accommodate up to 5000 visitors a day. There were open-air gyms (palaestrae), a dry heat sauna and massage room (laconicum), a hot room (caldarium), a warm room (tepidarium), a cold room (frigidarium) and an outdoor Olympic-sized pool for swimming (natatio) that was 164 feet long and just three feet deep.
The swimming pool had no roof and was heated by radiant panels, bronze mirrors angled above to the pool to reflect the sun onto it. The inside rooms and their pools were heated by a hypocaust, an underfloor heating system that channeled hot air from coal and wood-burning furnaces. The closer to the furnace the hotter the room. The water was supplied by a branch of the Aqua Marcia aqueduct called the Aqua Antoniniana built by Caracalla specifically for this purpose. The aqueduct ended in a giant cistern two stories high with 64 vaulted chambers where the water was collected. A series of underground channels carried it from the reservoirs through the hypocaust for heating.
The scale of these baths was so massive the tunnels which ensured its proper operation had to be as well. There are two miles of tunnels along three levels. Each tunnel is 20 feet high and 20 feet wide, wide enough for two ox carts to pass through side by side. Driven by armies of slaves, the carts would transport tons of wood a day to stoke the 50 furnaces.
The baths weren’t just for bathing, though. The complex also featured a public library with books in Latin and Greek, all kinds of shops and even conference rooms. The gardens were richly landscaped with plants, water features and sculptures. In fact, the Farnese Pope Paul III ordered the baths be excavated in 1545 with the hope that he could score some quality sculptures for the family collection. His dreams came true and then some. Among the treasures found Farnese Hercules and the Farnese Bull, both now in the National Archaeological Museum of Naples along with the rest of the Farnese sculpture gallery.
Even the tunnels had spaces dedicated to non-bath purposes. The largest Mithraeum in the world was built there. The mystery rites of Mithras were always held in natural caves or in dark underground spaces that resembled caves, and the Baths of Caracalla had room galore along those lines.
The baths remained in use until 537 A.D. when the city was besieged by the Ostrogoths under Witiges who cut off the aqueducts supplying Rome with its water. Since the baths were located at the base of the Aventine close to the southern city walls some distance from the historic center, the baths were left to their own devices during the post-imperial decline of Rome. They decayed into ruin but at least nothing was built over them. Over time people forgot about the complex system of tunnels that had once kept the water running hot; the excavations of the 1500s didn’t go down that far.
The palestrae with their elaborate mosaic floors were rediscovered the first half of the 19th century, and the rest of the complex was revealed over the course of multiple excavations throughout the rest of the 19th century and the first half of the 20th. The tunnels were not as glamorous as the topside finds, however, so even as the baths became a major tourist attraction, the guts of the complex remained off limits to visitors.
Mussolini attempted to strengthen them in the 1930s as part of his plan to use the ruins as a stage for operas. The first summer season opera, Donizetti’s Lucia di Lammermoor, debuted August 1st, 1937, on a stage 72 feet wide, the largest stage in the world at that time, built in the remains of the caldarium. The Rome Opera still puts on a summer season at the Baths of Caracalla to this day, although there was a break between 1940 and 1944 due to war and between 1994 and 2000 due to concerns that the productions were harming the structures. Now the operas are no longer held in the caldarium but rather on the grounds with the majestic remains as a backdrop.
Over the past year, a restoration program has finally paid some overdue attention to the tunnels. The program started inauspiciously with the installation of skylights in the roofs of the tunnels. This turned out to be a bad idea. As soon as the formerly sealed walls were exposed to sunlight and airflow, algae began to make a home for themselves. Within a few months the skylights were closed, the walls cleaned and an electric lighting system installed so tourists can see.
The Mithraeum opened to visitors last month and will remain open until January. There’s little of the decoration left — a partial fresco, the black and white mosaic floor, a piece of a marble altar — but its sheer size is remarkable. The tunnels where restoration is complete will remain open indefinitely. Restoration continues for the rest of the tunnels. The full restoration project is expected to take another two years.