Archaeologists also found several lengths of World War II tank tracks
A flint blade thought to date back about 4,000 years has been found near a Bronze Age site which is being covered by a road.
The blade, which has a serrated edge, was found by workmen near the Rotherwas Ribbon - an ancient path of stones in Herefordshire.
Campaigners fought to prevent a £20m relief road being built over them, but councillors rejected their calls.
A "protective membrane" will instead preserve it for future generations.
Campaigners had urged the council to abandon the road plans when the Rotherwas Ribbon was found and instead turn it into a tourist attraction.
However, Herefordshire Council said the projects were essential and would bring up to 700 new jobs to the area.
Archaeologists also found several length of tank tracks towards the east of the 14-acre site, which they believe are evidence of a World War II tank repair works.
The area was previously used by the Royal Ordnance during and after the war.