Archaeologists have unearthed at least 210 skeletons buried beneath the site that will soon become a new Marks & Spencer Simply Food store.
They are believed to date back to when the area behind Berkhamsted High Street’s former Royal Mail sorting office was used as a medieval hospital’s burial ground.
Remnants of discarded pottery found scattered around the site dates back to the 12th to 14th Century, said Herts County Council’s historic environment adviser Kate Batt.
She said: “It is intellectually a very important site, because it gives us an opportunity to access the population that was living in and around Berkhamsted during that period.”
The bones will now be used to access what jobs people in the area did by examining which, if any, muscles had grown large through exertion.
Archaeologists will also be able to discover the age of the people buried, how well fed they were, whether they suffered from diseases and whether they died in combat.
The former sorting office will be used by M&S and two other shop or restaurant units from spring 2014 after it is extended to the rear.
Documentary evidence had long shown that a medieval order of monks ran a monastery, church, hospital and burial ground in the area.
Hospitals in medieval times were used more to home the elderly or sickly children, rather than for emergencies.
Mrs Batt said about 210 skeletons had been found when she checked recently, just as excavation work was drawing to a close.
She said: “There are still quite a number of skeletons on site, but they will not be disturbed by the development, so they will be left in situ.”
The bones will be reburied after archaeologists have finished with them and the pottery fragments will be passed on to a museum in the area.