Among the Mithraea

A few weeks ago, I embarked on a journey that I had wanted to make for some time: a pilgrimage across the ancient Roman world in search of the remnants of the Mysteries of Mithras. Over the course of nearly two weeks, I traveled from Rome to northern Italy, into Slovenia, and across Austria into Switzerland, tracing the paths once walked by Roman soldiers, merchants, initiates, and priests of one of antiquity’s most fascinating mystery religions.

The journey reminded me that the Cult of Mithras was an international mystery school. It spread wherever Rome spread. From military frontiers to bustling ports, from underground shrines hidden beneath modern churches to isolated sanctuaries preserved in alpine valleys, Mithraism left its imprint across the empire.

Entering the Underworld

On May 4, I landed in Rome and spent the day simply walking the city and absorbing its atmosphere. Rome is overwhelming in the best possible way. Ancient ruins stand beside Renaissance churches, medieval alleys open into imperial forums, and every stone seems layered with history. Before diving into my research, I wanted time to simply orient myself and reconnect with the Eternal City.

The following day, I descended beneath the Basilica of San Clemente to visit one of the most famous Mithraea in the world. Standing underground beneath a medieval basilica, which itself was built atop earlier Roman structures, one experiences the literal layers of Roman history. The Mithraeum of San Clemente is one of the clearest surviving examples of how the cult operated within the hidden spaces of the Roman world.

The sanctuary itself preserves the familiar imagery associated with Mithras: the tauroctony, or bull-slaying scene, benches lining the ritual chamber, and the intimate cave-like setting symbolic of the cosmos itself. Unlike large public temples dedicated to Jupiter or Mars, Mithraea were intentionally enclosed and mysterious, meant to separate initiates from the outside world and immerse them within a sacred space.

Later that day, I visited the Roman National Museum collections housing Mithraic artifacts and reliefs. Seeing these objects in person rather than in photographs was invaluable. The details of the iconography, the craftsmanship, and the regional artistic variations all provide insight into how widely the cult spread and how adaptable it became throughout the empire.

On May 6, I explored Rome further before traveling to the Parco della Caffarella to visit Il Labirinto di Roma, which contains a replica Mithraeum and preserves part of the ancient subterranean environment that once existed around the city.

One of the most fascinating aspects of ancient Rome is that much of it existed below ground. Beneath the bustling imperial capital stretched a vast network of tunnels, quarries, cisterns, catacombs, and passageways. The Romans quarried enormous quantities of volcanic tufa and pozzolana from beneath the city to construct temples, baths, aqueducts, roads, and walls. Over centuries, these excavated spaces formed labyrinthine underground systems.

Some of these tunnels were later reused for religious purposes. Early Christians created catacombs within them. Storage chambers and water systems were carved into them. Some Mithraic sanctuaries may also have utilized these naturally cave-like environments, which aligned perfectly with the cult’s symbolism of the cosmic cave. For initiates descending into these shrines, the journey underground itself became part of the ritual experience - a symbolic movement away from the ordinary world and into the sacred mysteries.

The Gateway to Rome

On May 7, I traveled to Ostia Antica, the ancient port city of Rome. With a guide, I explored multiple Mithraic ruins scattered throughout the site.

Ostia was critically important to ancient Rome. As the empire’s primary harbor city, it served as the commercial lifeline of the capital. Grain from Egypt, olive oil from Hispania, wine, marble, spices, and other goods from across the Mediterranean flowed through Ostia before reaching Rome. Due to this constant movement of merchants, sailors, dockworkers, and soldiers, Ostia became one of the most cosmopolitan cities in the empire.

That cosmopolitan character made it fertile ground for mystery cults like Mithraism. Ostia contains one of the largest concentrations of Mithraea discovered anywhere in the Roman world. The cult thrived particularly among merchants, administrators, and military personnel connected to trade and transportation. Walking through these sanctuaries provided a powerful glimpse into how embedded Mithraism had become within the everyday life of Roman society.

Unlike isolated archaeological fragments in museums, Ostia preserves an entire urban environment. Streets, apartment buildings, baths, taverns, warehouses, and temples still stand in remarkable condition. As I walked those ancient roads, it became easier to envision the world in which Mithraic initiates once lived and worshiped.

The Crossroads of the Empire

On May 8, I traveled north to Aquileia, one of the most important cities of the Roman Empire that many people today have never heard of.

Founded in 181 BC, Aquileia became a major military and commercial center strategically positioned at the head of the Adriatic Sea. It served as a gateway between Italy and the Danubian frontier regions. Troops, merchants, diplomats, and travelers passed constantly through the city, making it one of the empire’s great crossroads.

Aquileia grew immensely wealthy and influential. At its height, it rivaled some of the largest cities in the Roman world. The city played a crucial role in defending northern Italy against invasions from the Balkans and Central Europe while simultaneously facilitating trade into the provinces.

This environment helped Mithraism flourish. The cult spread rapidly along military and trade networks, and Aquileia’s location made it an ideal center for the transmission of eastern religious traditions into the western empire.

The next day, I visited the museum housing Mithraic relics as well as the Basilica and surrounding ruins. Aquileia’s archaeological remains are extraordinary. Mosaics, columns, roads, foundations, and artifacts still reveal the immense importance the city once possessed. The juxtaposition of Christian basilicas rising amid older Roman remains also reflects the broader religious transformation of the empire during late antiquity.

Mithras on the Frontier

On May 10, I traveled onward to Ptuj, Slovenia (the ancient Roman city of Poetovio). Reaching the city required two buses and three trains, a reminder that even modern travel across Europe can sometimes feel like an expedition.

Ptuj is the oldest town in Slovenia and possesses deep Roman roots. Under the Romans, Poetovio became a major military settlement and administrative center along the Drava River. Legions were stationed there, trade flourished, and the city became an important strategic outpost on the empire’s frontier.

The area also became one of the strongest centers of Mithraic worship in the region. Numerous Mithraea have been discovered in and around Ptuj, reflecting the heavy military presence and the movement of eastern religious traditions through frontier zones.

After arriving, I visited Ptuj Castle and the archaeological park containing Roman ruins. The city carries an atmosphere unlike Rome. Whereas Rome overwhelms with imperial grandeur, Ptuj feels quieter and more intimate; a frontier town shaped by centuries of overlapping civilizations.

On May 11, I visited the preserved Mithraeum at Spodnja Hajdina across the river from Ptuj, where I was fortunate enough to receive a tour from an archaeologist. Experiences like this are invaluable. Speaking directly with specialists working to preserve and interpret these sites provides layers of understanding that books alone cannot offer.

Standing within an actual Mithraic sanctuary, one begins to appreciate the lived reality of the cult. These were not abstract symbols confined to academic discussions. They were active religious spaces where initiates gathered, performed rituals, shared sacred meals, and participated in a spiritual brotherhood that stretched across the Roman world.

That evening, I began the long overnight journey north through Graz and Zurich before finally reaching southwest Switzerland.

Mithras in the Alps

I arrived in Martigny on May 12. Nestled within the Swiss Alps, the town occupies another strategically significant Roman location. Ancient Martigny, known as Forum Claudii Vallensium, sat along important alpine trade and military routes connecting Italy to Gaul and Germania.

On May 13, I explored the museum, amphitheater, baths, domus, and Mithraeum preserved there. The Mithraeum of Martigny is particularly important because it demonstrates the extraordinary geographic spread of the cult. From the heart of Rome to the frontiers of Slovenia and the valleys of Switzerland, Mithraism followed the arteries of the empire.

The Roman remains throughout Martigny are beautifully preserved and offer another reminder that the Roman world was deeply interconnected. Ideas, religions, goods, and people moved constantly across enormous distances. 

Later that day, I returned to Zurich to prepare for my flight home, and on May 14, I departed for the United States.

Returning Home

Research trips are often romanticized, but they can also be exhausting. Long train rides, navigating unfamiliar cities, and operating on limited sleep become part of the experience. Yet every moment was worth it.

This journey gave me something that books and articles alone never could: context. Seeing the geography of the Roman world firsthand changes one’s understanding of how Mithraism spread and why it resonated with so many people. The cult was not isolated. It was woven into the military, commercial, and social fabric of the empire itself.

Now, after following the footprints of Mithras across Italy, Slovenia, and Switzerland, it is time to put my nose to the grindstone and finish my book on the Mysteries of Mithras. The journey may be over, but the work continues.