Two metal detectorists, Craig Best and Roger Pilling, have been jailed for attempting to sell Anglo-Saxon coins worth over £760,000.
The coins were buried by a Viking in the ninth century and are believed to be part of the Herefordshire or Leominster Hoard.
Two coins are still missing after being hidden by Best and Pilling.
The defendants were convicted of conspiracy to convert criminal property and possession of criminal property.
The coins were found in Leominster, Herefordshire, in 2015 and date back to 874-879 CE.
They include rare two-headed coins featuring Alfred of Wessex and Ceolwulf II of Mercia.
Best was arrested at a Durham hotel during an undercover sting operation, while Pilling was arrested at his home in Lancashire.
The coins have historical significance for the nation, and their loss would have been permanent if taken out of the country.
Four others have already been convicted and jailed for concealing the hoard.
Finders of potential treasure are legally obligated to report their discoveries under the Treasure Act 1996.