Four gold objects were discovered with 131 coins in a field in west Norfolk, most by the same anonymous metal detectorist who notified the appropriate authorities.
Ten coins were found by a serving police officer who tried to sell them and was jailed for 16 months. Norwich Castle hopes to acquire the “internationally significant” hoard.
Gareth Williams, curator of early medieval coins at the British Museum, said the “hugely important find”, which dates to the same era as the Sutton Hoo ship burial near Woodbridge in Suffolk, is “the largest coin hoard of the period known to date”.
The first coin was discovered in 1991, but it was not until 2014 that further coins, dating to about AD610, were found.
Some were minted in the Byzantine empire, but most were from the Merovingian kingdom, which broadly corresponds to modern day France.
Numismatist Adrian Marsden, from the Norfolk Historic Environment Service, said: “All the coins were minted on the continent, as we didn’t have gold coins of our own then.”