Two coins were uncovered by the rain on the lawn of farmer Tage Pettersson, on the island of Gotland, in early August. He called in Gotland's archaeologists, who last week found a further 52 coins on the site.
Most of the coins are German, English and Arabic currency from the late 900s and early 1000s. But archaeologists are most excited about the presence of six very rare Swedish coins, from the reign of Olof Skötkonug, king of Sweden from 994-1022.
One of the Swedish coins has never been found in Sweden before, although an example has been found in Poland. One of the other coins is only the second of its kind to have been found.
Archaeologist Dan Carlsson told Svenska Dagbladet that the coins were "very well preserved, and come from a period about which we know little in terms of coin history."
The English coins are likely to have been paid to the Vikings as an incitement to let them live in peace, he said.
Gotland is one of the richest sources anywhere of buried Viking treasure. Discoveries of coins and other treasure are made on a regular basis.