The coins will be sent to the British Museum for examination
Four silver coins dating from Norman England have been found in Gloucestershire.
It is believed they were minted in Gloucester in 1073-1076 and represent an unrecorded type of penny.
The coins were found by a metal detector enthusiast but details of the site have not been revealed.
Archaeologist Kurt Adams said the coins, which are just 0.8mm thick and about the size of a 10p piece, were incredibility rare.
Reports of the coins are already exciting collectors because of their rarity, Mr Adams said.
"Coins dating to the age of William I [William the Conqueror] are very rare finds, but these are unique," Mr Adams said.
"The finder reported them to me and I have taken them in under the 1996 Treasure Act and reported the find to the coroner who will hold a Court of Inquest to prove they are treasure.
"I'll then send the coins to the British Museum for examination.
"If experts there decide they want the coins they have to be independently valued and the museum would have to find the money."
"Half of that would go to the landowner and half to the finder.