The coins were found in two pottery vessels, buried 3m apart
One of the largest deposits of Roman coins ever recorded in Wales, has been declared treasure trove.
Nearly 6,000 copper alloy coins were found buried in two pots in a field at Sully, Vale of Glamorgan by a local metal detector enthusiast in April.
After the ruling by the Cardiff coroner, a reward is likely to be paid to the finder and landowner.
It is hoped the coins will be donated to National Museum Wales, which has called the find "exceptional".
Two separate hoards were found by the metal detectorist on successive days, one involving 2,366 coins and the other 3,547 coins, 3m away.
The 1,700-year-old coins dated from the reigns of numerous emperors, notably Constantine I (the Great, AD 307-37), during whose time Christianity was first recognised as a state religion.
Derek Eveleigh, 79, from Penarth, who came across the hoards in a field of sheep, has kept his find a secret until the outcome of the inquest.
He said: "I had a signal first and when it was deep I thought I better dig it - and that was it."
The coins now will be valued by an independent committee
Edward Besly, the museum's coin specialist called it an "exceptional find".
He said: "The coins provide further evidence for local wealth at the time. They also reflect the complex imperial politics of the early fourth century."
'Time of danger'
It is thought the two hoards were buried by the same person, possibly two years apart. A similar find was uncovered in the area in 1899.
"There was quite a bit of Roman activity in the area at the time, southwards from Cardiff Castle, where there was a Roman fort, to the Knap at Barry where there was an administrative building and there were farms in the Sully area," said Mr Besly.
"There's a human story there somewhere but it's intangible, we can't really get to it but certainly somebody buried two pots of coins."
"It could have been they were buried for safe keeping, possibly at a time of danger."
It is hoped the coins will be given over to the museum for further study and to go on public display.
Mr Eveleigh added: "All I found before was thrupenny bits and bits of metal.
"I have had to keep it quiet all these months. Someone told me that when you find one hoard you find two."
Also declared treasure by the coroner were two bronze axes from Llancarfan, Vale of Glamorgan.
Discovered in June 2008, they were buried together as a small hoard. The two complete bronze socketed axes have ribbed decoration and are examples of the south Wales type, dating to the late bronze age (1000-800 BC).