"It's fantastic," Lars Sjösvärd, the director of Gotland's museum told Radio Sweden.
The find was made last Thursday by a man working for the government as part of a project to reclaim Gotland's medieval past from the fortune hunters who arrive from other countries, as well as Sweden, to find treasure and sell it on the black market.
"It is of very big economic value," Lars Sjövärd said.
The silver coins from the end of the Viking period are said to come from western Europe including Germany and England and will attract interest from around the world.
The find is uncommon because coins are usually displaced by a farmer's plough but in this case, the bronze casket was too far down below the ground.