Undergound burial vaults containing human remains have been found under a development site in Sunderland.
Long-forgotten chambers below Villiers Street, in Sunniside, were discovered under a former Sunday school building – being demolished as part of the area's regeneration.
A number of the vaults are bricked up and it is not yet clear how many skeletons are in the chambers, though interment records show 409 people were buried at the site.
Archaeologists are busy documenting the rare find before the remains are removed and sent away for analysis.
The bones will be reburied in Bishopwearmouth Cemetery and the crypt will be filled in.
The work has been organised by Sunderland arc and the Sunniside Partnership.
Ben Hall, director of Sunniside Partnership, said: "The excavation of this site is an extremely sensitive process, which is why specialist archaeologists have been appointed.
"They are investigating all the material underneath the building and while this work is carried out the site has been screened, sealed and secured for health and safety reasons."
Matthew Town, project manager from contractor North Pennines Archaeology, said: "The work presents a rare opportunity to learn more about the lifestyles of people in 19th-century Sunderland."
The Sunday school building, part of a non-conformist Bethel chapel, was built around 1817 and extended in 1826, when the burial vaults were built north of the church.
The chapel building was demolished in 1978, leaving behind the Sunday school – and the hidden vaults.
The chambers were first uncovered when the building, most recently a garage, was being broken up by contractors.
The site has been earmarked for family housing, but independent councillor and heritage campaigner Peter Maddison and Arnie Sneddon, a history buff from Villiers Street, want to see the vaults left intact.
Mr Sneddon said a glass roof should be installed to allow people to see into the brickwork chambers.
Coun Maddison said: "Sunderland has a fantastic history and we have a duty to preserve it."
But Liz Hughes, senior project manager of owners, Sunniside Partnership, said there was no safe access to the chambers and it was not practical to keep the chambers as they are.
Archaeologists are on site until March and because human remains are involved the team had to get permission to go ahead from the Ministry of Justice.
The Sunniside Partnership and One North East say they are working with Sunderland City Council, archaeologists, English Heritage and Tyne & Wear Archaeology to ensure the project is handled with the utmost professionalism, care and respect.