Human remains have been uncovered by workers laying gas pipes alongside Durham City's toll road barrier.
The bones and skulls are thought to be medieval and may be part of an old graveyard attached to the nearby St Nicholas' Church.
Work has been suspended while archaeologists from the Tyne and Wear Museums Service investigate.
Durham County Council has withdrawn the road toll temporarily, although limited access to the city centre remains.
Archaeologist Jonathan McKelvey believes the area is the former graveyard of a 12th Century church which was demolished to make way for the present church, built in 1858.
Signs of disease
He said: "There are four rather mashed up skulls and a lot of disarticulated bones. It is a bit of a mess.
"That church dated right back to the 12th century so it is possible the bones date from then.
"We do know they predate the present church."
The remains will now be examined for age, gender and any signs of disease.
Archaeologists at the site expect to find further bones when the work restarts.
A £2 toll was introduced in October 2002 for drivers wanting to access Saddler Street near the historic cathedral.