The remains of a medieval stone wall likely to be at least seven centuries old may have been found under the Palace of Westminster, experts have said.
The structure, thought to be the original medieval Thames River wall which was believed to run under the Houses of Parliament, was unearthed during work to help restore the building.
Experts say it is likely to be at least 700 years old and is made from Kentish ragstone, a hard grey limestone quarried from Kent and used in the construction of the Tower of London and Westminster Abbey.
Over the summer and early autumn, specialists spent 4,850 hours examining 160 rooms and drilling boreholes up to 70 metres deep to assess ground conditions around the Palace.
The discovery came during a geotechnical borehole investigation in Chancellor’s Court, near the House of Lords chamber, before drilling was paused and the structure was assessed by archaeologists from the Museum of London Archaeology (Mola).
It is likely the second time that part of the medieval river wall has been found.
Medieval timber structures thought to be waterfront revetments were discovered in Black Rod’s Garden in 2015.
The newly discovered wall runs alongside the medieval location of the riverside. A small amount of material was removed for analysis before the site was sealed up to protect the structure.
Roland Tillyer, archaeologist with the museum, said: “It’s been really exciting being involved in the restoration and renewal of the Palace of Westminster. Mola has previously done work in Westminster, which located the medieval river wall in Black Rod’s Garden.
“We were expecting it might be present in this area and the borehole in Chancellor’s Court may have encountered it.
“The first few meters of the borehole sequence was as expected, post medieval dump deposits, which are quite soft, but then around 3.5 metres (12ft) we came across much harder material, including Kentish ragstone, mixed with a sandy mortar.”
The boreholes are part of an extensive programme of building investigations by the Houses of Parliament Restoration and Renewal Delivery Authority.
Archaeologists have been on-site to record any finds of historical significance to add to records of the Palace.
Since January, restoration and renewal programme teams have examined more than 2,089 spaces across the Palace.
Surveyors have been lifting up floorboards, drilling into walls and removing ceiling panels to look at wall cavities, the material make-up of the building and the weight-bearing of historic flooring.
Specialist teams have been inspecting the hundreds of miles of interconnected power cables, gas, water and heating pipes as well as outdated water and sewerage systems.
Lord Speaker, Lord McFall of Alcluith, said: “The Houses of Parliament are full of extraordinary history that is worth protecting for future generations, as this discovery demonstrates.”
Sir Lindsay Hoyle, Speaker of the House of Commons, said: “The Palace of Westminster is a treasure trove of history, and making sure this is properly conserved whilst also getting on with the vital job of restoring this unique place is a key priority.”
Patsy Richards, interim CEO, Houses of Parliament Restoration and Renewal Sponsor Body, said: “We expect more exciting finds from dozens of surveys carried out over the coming months.
“We are also working really closely with the teams who keep the palace running now.”
