Archaeologists have uncovered the remains of a Roman lead smelting site in a peat bog in Ceredigion.
Dating back about 2,000 years, Cambria Archaeology said mines in the Borth area could have supplied the heavy, bluish-grey metal for production.
It added that blocks of Welsh lead may have even been transported to other parts of the Roman Empire.
Last year, archaeologists hinted they had found a Roman "industrial estate", but until now had little evidence.
In June last year, Cambria Archaeology, from Llandeilo, unearthed a medieval track on the edge of Cors Fochno (Borth Bog) in Llancynfelyn, near Borth.
It described it as the best preserved example of its type in Wales.
Carbon dating carried out on fragments of wood from the site dated back to 900 or 1020AD.
But further probing by archaeologists uncovered evidence of lead smelting underneath the track.
They returned to the site at the end of May with students from the University of Birmingham, who helped last year, and specialists from Lampeter University.
Now, after analysing data, archaeologists are confident they have stumbled across something significant.
"In Wales, this is of national significance. To find two key sites on top of each other is rare", said project leader Nigel Page.
"We've found a furnace and lead smelting base and although we have to do further scientific dating, we think it probably dates back about 2,000 years.
"As it is today, lead was an important commodity in Roman times and it's possible blocks or ingots were stamped with the legion identification and sent to other parts of the empire".
Mr Page said lead mines dotted throughout the area could hold further evidence of a Roman lead industry.
"There a number of lead mines in the area and it's possible these date back to Roman times and supplied lead for production," Mr Page added.
The smelting site has now been backfilled, although photographs have been taken of the find.