The bones from seven skeletons have been found under a charity shop in Northumberland.
When workers began converting a former charity shop into flats they were not expecting to find the human remains.
Builders were digging out a pit at the former Scope charity shop and cafe on Beaumont Street in Hexham when they made the discovery on Wednesday 8 November.
Archaeologists believe the bones are medieval and are there because a chapel used to stand on the site.
Work had been taken place to convert three of the upper floors of the building, which used to be a branch of Newcastle Building Society, into flats. Workers were preparing to put in a lift when they made the discovery.
Allan Fenwick, director of building company Abbey View North East, said he was shocked to receive a phone call from his site manager telling him about the find.
Mr Fenwick told Hexham Courant: "I was driving to the site when I received the phone call. When I got there, I saw it and was shocked. I have been in the business for 40 years and never came across bones before, so I wasn't sure what to do when we found them.
"I am mostly office-based so naturally I wouldn't have had any experience seeing them, but my site manager has been a part of many projects around Newcastle - where they found numerous bones.
"It was really strange as we didn't dig that deep and they were all piled on top of each other. There were seven in total but separated parts.
"Luckily we had our archaeologist from the planning application who was able to help with the process of getting a specialist coroner's licence to excavate it. I thought we would have to get the police in - but that was not the case.
"I was also quite worried that it would stop our work for months but thankfully it was only a week or two that we paused everything, so we aren't behind at all.
"We know the site was the old St Mary's Church, so it makes sense that we discovered the skeletal remains.
"We are keen to work with Rocket Heritage and Archaeology to learn more about the discovery, who they were, what happened to them."
The remains had been carefully buried in graves but had been built over as Hexham expanded.
Technical director of Rocket Heritage and Archaeology, Liz Murray said: "We found partial skeletal remains of approximately seven separate individuals, most of which were in defined grave cuts. It is likely that they had been buried within, and under the floor of, a chapel that used to stand on the site - suggesting that the burials were medieval in date.
"Analysis is ongoing to find out more about these past inhabitants of Hexham and any further work at the site will be carried out under archaeological supervision."
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