A team of archaeologists from the University of Exeter has found a Roman fort dating from the 1st Century AD in fields in Cornwall.
Several items of pottery have been excavated
Several items of pottery have been excavated and a furnace which may have been used to smelt minerals.
Researchers said the find at Calstock, close to a silver mine, could show for the first time the Romans' interest in exploiting Cornish minerals.
Very little is known so far about the Roman occupation in Cornwall.
'Medieval documents '
The discovery could therefore mark an important step in piecing together this period of history.
Archaeologists became interested in the site when they found references in medieval documents to the smelting of silver "at the old castle" and "next to the church" in Calstock.
The team conducted a geophysical survey, which clearly showed the outline of a feature of a similar shape to another Roman fort recently found near Lostwithiel.
The fort is only the third found in the county
They started digging and found the shape of a Roman military ditch.
University of Exeter archaeologist Dr Stephen Rippon said: "The Roman army only stayed in the South West for a few decades after the Conquest, before moving on to Wales.
"This find could help us to understand whether they were merely keeping watch over the locals, or were actually interested in exploiting commercial opportunities in the region."
The two other known sites of Roman forts in Cornwall are also in the south east of the county.
One was discovered last year near Restormel Castle, Lostwithiel, and the other is at Nanstallon, near Bodmin.
Both sites are close to mineral deposits in areas associated with tin mining.