The London Mithraeum: a secret temple beneath Bloomberg Arcade

Place card

Place: London Mithraeum Bloomberg SPACE, 12 Walbrook, London EC4N 8AA.

Area: City of London.

Nearest station: Bank.

Period: built around the middle of the third century; excavated in 1954; returned to its original site in the twenty-first century.

Themes: Mithras, initiation, the lost Walbrook and post-war archaeology.

Access: museum site; check the official website for booking, opening hours and filming rules.

The setting

The working day is ending above Walbrook. Screens shine, office doors close and commuters cross the City. Downstairs the noise fades. Visitors descend towards the stone plan of a temple; the lights fall, mist appears and voices emerge from the dark. It is a modern interpretation, not a recording of an ancient rite, yet it captures the building's essential move: a passage from the public city into a controlled space for initiates.

In 1954 the scene was rawer. Redevelopment was beginning among bomb-damaged plots. Archaeologists had little time. On the last scheduled day, a marble head of Mithras came out of the soil. It helped explain a building whose identity had remained uncertain and turned a construction site into a national sensation. Tens of thousands queued to look into the excavation. For a few weeks, London's secret Roman temple became one of its most public places.

The story

Mithraism is one of the most compelling and most carelessly simplified religions of the Roman Empire. The Roman Mithras shared a name and distant ancestry with an Iranian figure, but the imperial cult cannot simply be described as a Persian faith carried west by legionaries. Its communities, images and rituals developed in the Roman world. Soldiers, administrators and merchants did take part, yet the phrase “secret religion of Roman soldiers” is too narrow.

Its defining image is the tauroctony: Mithras killing a bull, surrounded by a dog, snake, scorpion and other figures. Modern audiences naturally ask for a translation. What does every creature mean? No complete Mithraic scripture or ancient handbook survives to answer. Scholars have developed strong interpretations, including astronomical ones, but no final key exists. A video promising the “true secret of Mithras” offers confidence the evidence cannot support.

Mithraea were usually long rooms with a central aisle and raised benches. The architecture directed attention towards a cult image at the far end. Such spaces evoked a cave, whether physically underground or constructed inside another building. London's temple was built around the middle of the third century on the eastern side of the Walbrook, one of the rivers now hidden beneath the City. By then its wet valley had already been reshaped by generations of building.

Why this exact site was chosen is unknown. There is no membership register and no founder's account. A connection with Londinium's commercial and administrative world is plausible, but the modern financial setting does not prove that Mithras was specifically a “god of bankers and contracts”. That is a neat present-day metaphor, not an established ancient fact.

The archaeological phases show change. Historic England dates construction to the mid-third century and use into the late fourth. In the early fourth century the building was probably adapted for another cult, conventionally linked with Bacchus or Dionysus. Scholars debate the sculptures and the transformation. The responsible conclusion is more intriguing than a frozen “secret temple”: religious use changed over time.

After Roman government ended, the ruin disappeared beneath later London. The Walbrook became a drain and was eventually covered. Medieval and early modern streets accumulated above it. Then bombing opened the twentieth-century city, and post-war clearance allowed W. F. Grimes and his team to investigate the site.

The 1954 discovery became a landmark in British urban archaeology. At first the walls were difficult to identify securely. Sculpture, including the head of Mithras, clarified the interpretation. Press coverage drew crowds and preservation became a political issue. The episode exposed a permanent London conflict: land is immensely valuable, redevelopment is urgent and archaeology appears late in the programme.

The compromise was imperfect. The remains were dismantled and reconstructed in 1962 roughly a hundred metres away, above their ancient level and with alterations. The monument escaped total destruction but lost context. In archaeology, position, orientation, elevation and relationship to a river are evidence, not scenery.

Another chapter began with Bloomberg's European headquarters. Excavations from 2010 to 2013 explored a much larger area. Waterlogged Walbrook soil preserved an extraordinary collection of organic material, including more than four hundred writing-tablet fragments. The project brought the temple back close to its original position and level. Stones were dismantled again, studied and incorporated into the presentation opened in 2017.

Visitors do not see an untouched third-century interior. They see a carefully designed presentation of archaeological remains. Ancient fabric survives, while wall heights, lighting, sound and mist suggest lost volume. This raises a valuable question: should a museum show only what physically remains, or may it also create an experience of missing space? The Mithraeum sits deliberately between ruin, reconstruction and theatre.

Its history is therefore larger than Roman religion. It is also a story about modern attitudes to buried heritage. In 1954 public pressure demanded that ruins be visible; the result preserved stones while dislocating them. The later project valued original context more strongly and used digital interpretation. Future curators may make different choices again. Every presentation reveals the period that produced it as well as the antiquity it describes.

People to remember

The discovery is often reduced to Grimes and the fortunate marble head. Excavation depended on labourers, surveyors, photographers and archaeologists, including the important contribution of Audrey Williams. The public mattered too. Londoners queuing among post-war ruins turned archaeological preservation into a civic question.

The ancient worshippers remain anonymous. We do not know who sat on the benches, who paid for the room or what initiation meant to a particular member. That absence is not a weakness to conceal with invented detail. It is the central mystery of the place.

Fact, interpretation and legend

Documented: the temple was constructed in the mid-third century beside the Walbrook; its form is characteristic of a mithraeum; the 1954 sculpture helped establish its dedication; remains were moved and later returned to the original site; today's display is a reconstruction.

Disputed: exact ritual content, membership, every element of the tauroctony and the religious identity of the altered fourth-century building.

Myth: Mithraism was simply a Roman version of Christianity; only soldiers could join; bulls are proven to have been sacrificed inside this temple; the modern sound-and-light sequence reproduces a known ancient ceremony.

The place today

Film the movement from surface to depth: corporate Walbrook, the entrance, objects in the upper display and then the darkened temple. State explicitly that the current atmosphere was designed. A strong final shot returns to the street with the thought that a lost river and a hidden sanctuary still shape a space in which neither is visible.

Research bibliography

[S0005] London Mithraeum Bloomberg SPACE, “About” — https://www.londonmithraeum.com/about/

[S0006] Historic England, “Temple of Mithras” — https://historicengland.org.uk/listing/the-list/list-entry/1391846

[S0007] Cambridge University Press, “When Things Don't Fit: Looking at the London Mithraeum” — https://www.cambridge.org/core/journals/journal-of-classics-teaching/article/when-things-dont-fit-looking-at-the-london-mithraeum/96304E44B06C1CE3D3248E2184281DE7