The London Mithraeum

Published 21 September 2026 · By the Guide to London editorial team · Editor: Terje Moy

The London Mithraeum is a Roman temple rebuilt seven metres below the pavement in the basement of Bloomberg's European headquarters, and it costs nothing to see. Allow an hour, not twenty minutes: the museum's own guidance is that a self-guided visit takes about that long, and the temple itself only opens to a new group every twenty minutes.

The building above is a bank's office block near Bank station. Go through the doors at 12 Walbrook, past a wall of Roman objects and a contemporary art installation, and a staircase takes you down two floors to the remains of a third-century temple to the god Mithras, laid out on the ground where it was found. A short sequence of light, haze and sound plays across the stones, and then the room is yours for a few minutes.

It is one of the strangest free things to do in the Square Mile, and it slots into a morning without much trouble. This page covers the practical side that decides whether the visit works: the twenty-minute cycle, the four different sets of opening hours, whether you need to book, and what is genuinely worth reading before you go down.

Three floors, and what happens on each one

The visit is arranged as a descent, and it is worth treating it that way rather than rushing for the temple.

At street level there is a space for the contemporary art commissions the museum shows alongside the archaeology. These change, so what you see will not be what the last visitor saw. Do not skip it on the assumption that it is a lobby.

The mezzanine below holds the objects. Several hundred finds from the excavation are set into a long display wall, and this is where the site stops being an abstraction: leather shoes, styluses, coins, amulets, the small litter of a working Roman town. There are 3D models that visually impaired visitors are encouraged to handle, and the hosts will describe objects and put them in context if you ask.

The bottom floor is the temple. You enter as a group at the set time, the lights go down, and the reconstruction runs. Then the haze clears and you are free to walk around the stones and look for as long as you like before going back up.

The twenty-minute clock is the thing to plan around

This is the single detail that catches people out. The temple is not continuously open. Groups go in on the hour, at twenty past and at twenty to, and if you arrive at nine minutes past you will wait eleven minutes upstairs.

That is not wasted time if you use it on the display wall, which is why the museum's hour-long estimate is realistic rather than generous. If you have only half an hour, you will see the temple and almost nothing else, and the objects are half the point.

Do you actually need to book?

No. The museum states that pre-booked tickets are not required, but encourages visitors to reserve a free ticket beforehand so that entry at a chosen time is guaranteed. In practice that means a walk-in works on a quiet weekday and is a gamble at lunchtime, at the weekend, and in school holidays.

Booking costs nothing and takes a minute, so there is no good reason not to. Groups no longer need a different ticket type; the standard visitor ticket covers them. School visits book separately.

If you are already in the area and find the next slots full, the walk to Leadenhall Market or to the ruined churchyard at St Dunstan in the East fills an hour easily, and both are free.

Four different opening patterns in one week

The hours are more complicated than most small museums, and the published timetable has four separate rules running at once.

It also shuts for 25 December, 26 December and New Year's Day. The term-time Wednesday rule is the one that spoils plans, because "term time" is not a date you can look up on the ticket page; if Wednesday morning is your only window, check the booking calendar before you travel across town.

The first-Thursday late opening is genuinely useful. The City empties after six, the last slots are quiet, and a temple lit in the dark below an empty office building is a better experience than the same temple at noon. Our round-up of museum late openings has the other evenings worth knowing about.

Why the temple spent decades in the wrong place

The stones were found in 1954, during the clearance of a bombsite left by the Blitz of 1941, by the archaeologist W. F. Grimes. On the last planned day of the dig a marble head of Mithras came out of the rubble, which settled what the building was. The discovery became national news, the dig was extended, and tens of thousands of people queued in the street to look at it. Historic England calls it one of the most important and popular archaeological discoveries of the immediate post-war years.

What happened next is the part that explains the museum. The site was needed for an office block, so in 1962 the temple was partly taken apart and rebuilt using the original fabric about 75 metres to the north-west and some six metres higher, on a terrace on Queen Victoria Street. Its orientation was changed in the process. It sat there for decades at pavement level, in daylight, looking more like a garden feature than a temple.

When Bloomberg began building here in December 2010, the archaeology came with the plot, and the temple was brought back to the spot where Grimes found it and put at Roman ground level. That is why the room you stand in is below the modern street: the Roman city is simply that far down.

The reconstruction you see is a recreation rather than an untouched ruin, and the museum says so plainly. The sound and light sequence is set in London around AD 240, with footsteps, chanting and whispers. Some visitors love it and some find it theatrical; either way it lasts a few minutes, and the stones are still there afterwards.

Mithras, and why the cult met underground

The cult of Mithras first appeared in Rome in the first century AD and spread across the empire over the next three hundred years, mainly among merchants, soldiers and imperial administrators. Its temples were often built below ground: private, dark, windowless rooms. The central image is the tauroctony, Mithras killing a bull inside a cave, and its full meaning is still argued over.

That matters for how the site feels. A Mithraeum was never meant to be a public building with a grand front. It was a small, closed room for a group that kept its business to itself, which is why a windowless basement under a bank is, oddly, the right setting.

The temple here was built around AD 240 to 250, roughly two hundred years after Londinium was founded, on reclaimed ground beside the Walbrook, one of London's buried rivers. Historic England's listing records that it was probably rededicated to Bacchus in the early fourth century, fell out of use later that century, and then stood as a ruin into the Anglo-Saxon period. It remains the only Mithraeum known from Roman London and one of a handful found anywhere in Roman Britain.

If that thread interests you, our guide to what survives of Roman London covers the wall, the amphitheatre and the rest.

The writing tablets, and the first mention of London

The excavation that preceded the Bloomberg building produced more than four hundred fragments of Roman waxed writing tablets, recovered by archaeologists from MOLA. According to the museum it is the largest and earliest such collection found in Britain, and it contains the first known written reference to London along with the earliest hand-written document from these islands.

These were everyday objects: notes, accounts, letters, legal paperwork. They are the reason the site is treated as one of the most important archaeological excavations in the country, and a free illustrated guide to the research on them can be downloaded from the museum's website.

Only a selection of the finds is on the display wall at any time. If the tablets are the reason you are coming, read the guide first, because the objects reward knowing what you are looking at far more than they reward staring at them.

Getting to 12 Walbrook, and what is not there

Cannon Street station is a minute away, Bank about two minutes and Mansion House about six. St Paul's is a ten-minute walk, Blackfriars twelve, Liverpool Street fourteen and London Bridge eighteen. Bank is a large and confusing interchange, and the walk between its platforms takes longer than the map implies; our Underground guide sets out how the lines meet there.

There is step-free access to every floor by lift, all floors take a wheelchair, the accessible toilet is on the ground floor, assistance animals are welcome and there is seating throughout. Large-print and Braille texts are available, and printed transcripts accompany the audio. The temple sequence uses low light, lighting effects, mist and sound, so check that it suits everyone in your party before you book; our accessible London guide sets the City in a wider context.

Two things are not there. There is no café or eating area on site, and suitcases, large rucksacks and bikes are not allowed in, with only limited buggy storage. Flash photography and video are prohibited in the temple itself. For food, Bloomberg Arcade is next door, and Watling Street, a Roman road that has been restored and pedestrianised, runs alongside it with a row of independent places.

Half a day built around it

An hour here leaves most of the morning, and the City packs a great deal into a short walk. The Roman amphitheatre under Guildhall Art Gallery is about ten minutes north and also free, which makes the pair of them a coherent Roman morning. The Bank junction and the Royal Exchange are on the way.

For a view rather than a basement, the Sky Garden is free with a ticket booked in advance, and the Monument charges a small fee for 311 steps. If it is raining, the City's churches are the obvious shelter, and All Hallows by the Tower has Roman pavement in its undercroft.

Further out but on the same theme, the Museum of the Order of St John in Clerkenwell is another free small museum with a much older building attached, and the new London Museum opens at West Smithfield on 28 November 2026. Our list of free museums across London and our wider guide to things to do that cost nothing both have more. If the rest of your day is a big paid attraction, read our timings for how long the Tower of London takes before you commit to both.

Frequently asked questions

Is the London Mithraeum free?

Yes. Admission costs nothing, and the museum says plainly that it is free to visit. Reserving a slot online beforehand holds a place for you, but no ticket is required and walk-ins are taken when there is space. Donations are not demanded at the door.

How long does the London Mithraeum take?

The museum says a self-guided visit takes approximately one hour. That covers the contemporary art space at street level, the wall of Roman finds on the mezzanine, the wait for your twenty-minute temple slot and the temple experience itself. Half an hour is enough only for the temple.

Do I need to book London Mithraeum tickets?

Not strictly. The museum encourages advance booking so that your chosen time is held for you, and that matters at weekends, at lunchtime and during school holidays. On a quiet weekday morning you can usually walk in, though the next twenty-minute temple entry may be a short wait away.

Is the temple the original Roman one?

The stones are original, but the layout is a faithful reconstruction rather than an undisturbed ruin. The temple was found in 1954, moved to Queen Victoria Street in 1962 and rebuilt on its original site at Roman ground level when Bloomberg developed the plot. The museum is clear that it is a recreation.

Is the London Mithraeum suitable for children?

Older children who like archaeology usually take to it, and the display wall of everyday Roman objects works better with them than a case of statues would. The temple sequence is dark, with haze and recorded voices, so it can unsettle very young children. There is limited buggy storage and no café.

Sources

• London Mithraeum Bloomberg SPACE - Plan your visit (checked September 2026)
• London Mithraeum Bloomberg SPACE - Free admission and opening hours (checked September 2026)
• London Mithraeum - Temple of Mithras (checked September 2026)
• London Mithraeum - About: the 1954 discovery and the writing tablets (checked September 2026)
• Historic England - Temple of Mithras, National Heritage List entry 1391846 (checked September 2026)