An archaeologist believes he has discovered the remains of a Roman quarry in the old harbour at Barry in the Vale of Glamorgan.
Karl-James Langford says the pottery find reinforces his belief that beach man-made walls may be 1,900 years old.
The quarry was operational until the 19th Century but its origins were unknown.
"It's not in the records - it may have been been completely ignored because it's too obvious," said Mr Langford.
He believes the quarry to be the source of limestone used for the Roman fort whose remains can be seen in the walls around Cardiff Castle, although historical records do not mention such a quarry.
"I've had this belief that there was a Roman quarry there all my life," said Mr Langford, a landscape archaeologist from Barry.
He said a wall of unquarried high-quality lias limestone left in place on the beach was evidence of a quarry, similar to larger examples along the coast at Porthkerry, Rhoose and Aberthaw.
People would have been able to extract the material behind the wall at any time, without being engulfed by the sea.
A discovery during a recent expedition with students convinced Mr Langford of the quarry's Roman origins.
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