Finders are not always keepers as metal detectorists and coin dealers in Britain have learned.

Four men face years of incarceration for failing to report Viking treasure worth an estimated $3 million.

Police say the find has national importance for Anglo-Saxon coinage and for a greater understanding of a critical time in British history. Some of the recovered coins are helping scholars rewrite history, according to police.

Thirty-eight-year-old George Powell, 51-year-old Layton Davies, 57-year-old Simon Wicks and 60-year-old Paul Wells were all found guilty by the Worcester Crown Court of theft, conspiracy to conceal criminal property and conspiracy to convert criminal property, according to West Mercia Police.

Investigators were tipped off to the men’s findings by the metal detecting community in June 2015, according to police.

Powell and Davies had made their discovery in Herefordshire, an agrarian county in the West Midlands of England that is best known for its beef cattle and cider production.

When the men found the treasure, they didn’t notify the farmer who owned the field or the authorities, BBC reported. Instead, they contacted antiquities dealers and the National Museum Wales, to which they only declared one coin each and three pieces of jewelry. Only 31 of 300 coins reportedly in the treasure trove have been recovered, according to the British broadcaster.

After sifting through the treasure, experts found that the men had also uncovered a pendant made from a sphere of rock crystal and bound with gold, a gold ring, a gold arm band and silver bars and coins, according to police. The coins were typical of Viking use in the 9th and 10th centuries in Britain.

Authorities say there are outstanding coins from the loot, and they are urging other metal detectorists and coin dealers to contact them if they’ve seen or heard about the Viking coins.

An ancient Viking might have hidden the riches to protect them, according to Gareth Williams, curator of medieval coins and Viking collections for the British Museum, in an interview with CNN.

Not reporting found valuable items is a crime under British law.

Under the Treasure Act of 1996, finders are required to report their treasures to the local coroner’s office within 14 days of their discovery. The coroner would then consult museum authorities to ascertain the items’ value. If the objects are deemed to be treasure, the secretary of state would then determine whether a reward should be paid to the finder, which would be whoever occupied the land at the time of the discovery or any person who had interest in the land at the time of a finding, according to the law. Discoverers can be paid up to the treasure’s market value.

The British government has paid a metal detectorist before.

In 2001, a man named Cliff Bradshaw literally struck gold while out on a metal detection excursion on a farm in a village of Kent. He uncovered one of the earliest treasures found in England: the Ringlemere Cup. The Bronze Age item, now housed at the British Museum, paid more than $500,000, an amount split between Bradshaw and the farm’s landowner, according to the BBC.

In 2014, metal detector enthusiast Derek McLennan uncovered hundreds of silver and gold 9th- and 10th-century Viking pieces on Church of Scotland land that was worth more than $2.5 million, the Sunday Post reported.

While the law applies across Britain, Scotland allows for finders to keep all of their rewards without splitting it with the property owner, so McLennan was planning on keeping his riches to himself — backpedaling on an alleged agreement he made with the Church of Scotland to split the money, the paper reported.

The church launched a lawsuit in September to get its half.

Metal detecting as a hobby has seen a resurgence in popularity since the British Museum revealed a record number of treasure finds in 2016, the Guardian reported.

Britain has the most generous system in the world for rewarding finders, said Williams, the British Museum curator, in a quote given to police.

Judge Nicholas Cartwright told the four convicted men on Thursday they had cheated the public and that the “irony in this case” was they could’ve reaped up to half the value of their found goods among themselves if they had followed the law, the BBC reported.

“The treasure belongs to the nation,” he told them.

Powell will serve 10 years in prison, Davies will do 8½ years and Wicks will spend five years behind bars for failing to report Viking treasure. Wells will receive his sentence Dec. 23, according to police.

The local commander of Herefordshire police, Superintendent Sue Thomas, said she hopes what happened to the guilty men will serve as a warning to the metal detecting community about reporting their discoveries.

“I hope this demonstrates how seriously we take this sort of crime in Herefordshire and it is a criminal offense to not declare finds of treasure to the local coroner’s office,” Thomas said in a statement.

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