A group of people trawling a British field with metal detectors stumbled upon the find of a lifetime: a treasure trove of silver coins dating back nearly a millennium.

The British Museum revealed the find Wednesday, calling it the largest hoard of coins ever to be discovered from the immediate aftermath of the 11th-century Norman conquest of England.

The cache comprises 2,528 coins and some additional fragments. Many of them depict Harold II, the Anglo-Saxon king who was deposed during the conquest, or his successor, William the Conqueror. In both cases, the discovery represents far more coins than were previously known to exist of either ruler.

The coins were discovered in January in Somerset, west of London, by a group of metal detector hobbyists. The coins have spent the past seven months at the British Museum, where they have been cleaned, catalogued and researched.

It is believed the hoard was likely buried sometime around 1067 or 1068, shortly after the 1066 conquest. While it is not clear why it was buried, it is possible that the coins' owner hid them to protect them against raids from people loyal to Harold II.

Particularly exciting to researchers is the first evidence ever found of a "mule" – coin talk for a piece with different design types on each side. The museum likens this to "an early form of tax evasion," saying it allowed the coin producer to reuse an old die, avoiding the fee that would come with purchasing a new one.

Museum officials say the coins are generally in good condition. Efforts are now underway to determine if they can be legally classified as treasure, which would give museums the opportunity to acquire them and allow for a reward to be paid to the finders and the owner of the land where the discovery was made.

No official valuation of the coins has been made. Adam Staples, one of the people involved in the discovery, said he had been told that the find could be worth more than 5 million pounds ($8.1 million), according to the Press Association.