The Roman temple, when it was originally built, would have stood on the east bank of the now covered-over River Walbrook, a key freshwater source in Roman Londinium.
Nearby, in its former streambed, a small square hammered lead sheet was found, on which an enemy of someone named Martia Martina had inscribed her name backwards and thrown the token into the stream, in a traditional Celtic way of reaching the gods that has preserved metal tokens in rivers throughout Celtic Europe, from the swords at La Tène to Roman times (compare wishing well.)
The temple foundations are very close to other important sites in the city of London including the historic London Stone, the Bank of England and London Wall.
The original Mithraeum was built partly underground, recalling the cave of Mithras where the Mithraic epiphany took place.

The temple site was uncovered in September 1954 during excavation work for the construction of Bucklersbury House, a 14-storey modernist office block to house Legal & General.
As a compromise between redesigning the new building and abandoning the archaeological site, the ruin was dismantled and moved 100 metres to Temple Court, Queen Victoria Street, where in 1962 the foundations were reassembled at street level for an open-air public display.
The reconstruction was not accurate and drew criticism for the materials used.
An interim report on the excavation included in W. F. Grimes, The Excavation of Roman and Mediaeval London (1968) was superseded by John Shepherd, The Temple of Mithras, Walbrook (an English Heritage monograph) (1998).

In 2007 plans were drawn up to return the Mithraeum to its original location, following the demolition of Bucklersbury House and four other buildings in the block for the planned creation of a new Walbrook Square development, designed by Foster and Partners and Jean Nouvel Architects.
However, redesigns and disputes between freeholders Legal & General and Metrovacesa, who had agreed to buy the project, resulted in the Walbrook Square project being put on hold in October 2008, when Bovis Lend Lease removed their project team.
 Metrovacesa left the project in August 2009.
 In May 2010 the Mithraeum remained in situ at Temple Court, though in the same month there was talk of reviving the Walbrook Square project.

The Walbrook Square project was purchased by the Bloomberg company in 2010, which decided to restore the Mithraeum to its original site as part of their new European headquarters.
The new site is 7 metres (23 ft) below the modern street level, as part of an exhibition space beneath the Bloomberg building.
The temple was moved a little west of its original position to preserve parts of the walls that were not uncovered in 1952–54 and are too fragile to display today.

The ruins are reconstructed as they appeared at the end of the excavation in October 1954, reflecting the first building phase of around AD 240 without any later Roman additions to the site.
A large majority of the stones and bricks are original.
The wood, render and lime mortar are new, but based on mortar samples from contemporary Roman London structures.
The temple is displayed with a selection of artefacts found on the site.
The Roman temple, when it was originally built, would have stood on the east bank of the now covered-over River Walbrook, a key freshwater source in Roman Londinium. Nearby, in its former streambed, a small square hammered lead sheet was found, on which an enemy of someone named Martia Martina had inscribed her name backwards and thrown the token into the stream, in a traditional Celtic way of reaching the gods that has preserved metal tokens in rivers throughout Celtic Europe, from the swords at La Tène to Roman times (compare wishing well.) The temple foundations are very close to other important sites in the city of London including the historic London Stone, the Bank of England and London Wall. The original Mithraeum was built partly underground, recalling the cave of Mithras where the Mithraic epiphany took place.
The temple site was uncovered in September 1954 during excavation work for the construction of Bucklersbury House, a 14-storey modernist office block to house Legal & General. As a compromise between redesigning the new building and abandoning the archaeological site, the ruin was dismantled and moved 100 metres to Temple Court, Queen Victoria Street, where in 1962 the foundations were reassembled at street level for an open-air public display. The reconstruction was not accurate and drew criticism for the materials used. An interim report on the excavation included in W. F. Grimes, The Excavation of Roman and Mediaeval London (1968) was superseded by John Shepherd, The Temple of Mithras, Walbrook (an English Heritage monograph) (1998).
In 2007 plans were drawn up to return the Mithraeum to its original location, following the demolition of Bucklersbury House and four other buildings in the block for the planned creation of a new Walbrook Square development, designed by Foster and Partners and Jean Nouvel Architects. However, redesigns and disputes between freeholders Legal & General and Metrovacesa, who had agreed to buy the project, resulted in the Walbrook Square project being put on hold in October 2008, when Bovis Lend Lease removed their project team.  Metrovacesa left the project in August 2009.  In May 2010 the Mithraeum remained in situ at Temple Court, though in the same month there was talk of reviving the Walbrook Square project.
The Walbrook Square project was purchased by the Bloomberg company in 2010, which decided to restore the Mithraeum to its original site as part of their new European headquarters. The new site is 7 metres (23 ft) below the modern street level, as part of an exhibition space beneath the Bloomberg building. The temple was moved a little west of its original position to preserve parts of the walls that were not uncovered in 1952–54 and are too fragile to display today. 
The ruins are reconstructed as they appeared at the end of the excavation in October 1954, reflecting the first building phase of around AD 240 without any later Roman additions to the site. A large majority of the stones and bricks are original. The wood, render and lime mortar are new, but based on mortar samples from contemporary Roman London structures. The temple is displayed with a selection of artefacts found on the site.
London Mithraeum