More than 600 silver coins found on an Anglesey beach by a metal detectorist have been declared treasure trove by a coroner.
It is thought the coins could be worth around £4 each
The haul, dating from around 1272 will be valued before the finders are paid, and the items offered to the National Museum of Wales.
The coins were collected over a six-year period at an undisclosed area of Llanddona beach.
The Llangefni inquest heard it is a mystery how they ended up there.
It is an offence not to report discovered treasure to a coroner.
On Thursday, North West Wales deputy coroner Nicola Jones considered more than 600 coins which were part of a larger haul discovered by enthusiasts Graham Williams from Northop Hall in Flintshire and Chris Andrews from Guilden Sutton, Chester.
In all, they have discovered more than 900 coins at the secret location.
During one visit the men were walking back to their car empty-handed when Mr Williams' metal detector picked up a signal. They began digging and found 311 coins.
An expert from the National Museum of Wales confirmed the silver pennies were of the same type - mostly from England between 1272 and 1307, but also from Scotland, Ireland and Europe.
Part of a previous haul is already in the ownership of Oriel Ynys Môn in Llangefni, and the museum has also shown an interest in adding the latest coins to their collection, the inquest heard.
Mr Andrews, a semi-retired nuclear physicist, said: "We've always been lucky on our trips to Llanddona.
"Sometime we've found them in groups, sometimes singly, and we still don't really know how they got there."
Mr Andrews said some of the coins got his heart "pounding"
Coins were usually found along with something else which suggested how they got there, he added, but the Llanddona coins were a mystery.
"We've found around 970 in total, but the sandbank has moved over the last winter to cover the spot and we've failed to find anything else there recently."
The treasure hunters must now wait for the coins to be officially valued, but Mr Andrews guessed they could be worth around £4 each.
"They aren't worth a great deal of money but as a scientist I am fascinated as to how they got there," he said.
"The coins are sandwiched between a layer of sand and a layer of packed shells - it's a mystery how they got there."
In a separate inquest the coroner decided a thirteenth century silver brooch, medieval brooch fragment and a post-medieval signet ring found near Beaumaris were all treasure trove.