"These are exciting findings that raise several questions," says Johan Rönnby, professor of marine archaeology at Södertörn University.
He believes that it could be about the remains of a wrecked ship, maybe the coins can be linked to trade in seal trans products? Lots of remnants of fireplaces have previously been found on the coast of Sandön.
In the late 1800s, a lighthouse keeper named Hjalmar Söderberg said that he had found a Roman coin on the island. It was then met with skepticism. The finds of coins now in March say he might have been right.
"If the coins come from a wrecked ship, it means that there are probably more things to find on the embankment. Even more exciting.
Hear more about the spectacular find in the video above.