"Someone else's grave" refers to the grave where one of the two treasures now on display - the Sundveda treasure - was found in 2008.
The excavations started because the new Steningehöjden district between Märsta and Sigtuna was to be built.
They wanted to make sure that no antiquities went to waste.
The treasure that came to light turned out to be 452 silver coins that Vikings brought home after their trading trips.
Cunning hiding place
That they were hidden in a tomb may have been a cunning trick to prevent others from finding and stealing them.
- People were a little afraid of graves, says Ted Hesselbom at the Sigtuna museum.
Whether the explanation is correct or not we will never know – the coins are estimated to be from the 8th century and there are no written sources that tell us exactly why the coins were placed in the tomb.
Video: Come along to the exhibition - and hear from the archaeologist who made the find of a lifetime.