A large, well-preserved silver hoard from the early Middle Ages was discovered in Sweden and reported to the Stockholm County Administrative Board, which immediately began an archaeological excavation.

Experts estimate the treasure could contain up to 20,000 coins, mostly dating to the 12th century, including rare “bishop’s coins” and coins minted under King Knut Eriksson.

The hoard was buried in a copper cauldron, likely during late-12th-century unrest when Sweden was expanding into Finland, and predates the founding of Stockholm itself, Archaeology News has reported.

Archaeologists are documenting and analyzing the find, with the Swedish National Heritage Board deciding if the state will claim it, while the honest finder may be compensated under the Cultural Environment Act.