A man digging his back garden in Cardiff uncovered Roman pottery, which has prompted months of excavation.
The National Museum of Wales has helped verify the pottery finds
The find at the house on the Pentrebane estate is the first evidence of Roman activity in this part of the city.
Archaeologists have so far uncovered 300 pieces of pottery shards which they believe date back nearly 2,000 years and could be a manufacturing site.
The homeowner alerted them after thinking there was something unusual about the pottery.
Archaeologist Graham Oxlade, one of the team working on the discovery, said the find was of huge significance for the area.
"It's really important because up to this point there was nothing known from the Pentrebane area of the Romans around the area," he told BBC Radio Wales.
"It was unbelievable. When I went up there, you expect to see a couple of pieces of later pottery but when I looked at it, every piece was Roman.
"It's [a site] for manufacturing. What we have got is the flow from the drainage soakaways."
He said they had uncovered 300 pieces "and counting" of pottery in an area with no previous evidence of Roman occupation.
The excavation is nearing completion following eight months of work. As well as pottery, the team has found hobnails from Roman sandals and building nails.
Mr Oxlade said iron found on the site could indicate a smelting workshop nearby.
Some of the pottery is a type known as Samian ware, which was imported from Gaul, modern-day France.
Cardiff's best-known Roman site is a castle on the site of the present Cardiff Castle in the city centre.
South Wales held two important sites for the Romans, with the barracks at Caerleon, near Newport, and the old Roman town of Venta Silurum at Caerwent.
The homeowner does not want to be named to keep the site private.
He made his discovery after he removed a few feet of topsoil from his garden and discovered pieces of a Roman roof tile.
He said he was already interested in archaeology and was delighted with the find, adding: "The idea I could walk out from my patio onto a site was like winning the lottery."
Mr Oxlade thinks finds such as this by members of the public could be crucial to archaeologists.
"We want to get a wide picture of what was happening in Wales, whether it's Roman or Victorian because whatever's found in the ground has got a story to it.
"It's up to us to determine the right story."