The historic Viking trading centre of Birka, on Björkö in Lake Mälaren, makes a fantastic day trip. A Unesco World Heritage Site, it was founded around AD 760 to expand and control trade in the region. The village attracted merchants and craft workers, and the population quickly grew to about 700. A large defensive fort with thick dry-stone ramparts was constructed nearby.
Birka was abandoned in the late 10th century when Sigtuna took over the role of commercial centre.
The village site is surrounded by the largest Viking-age cemetery in Scandinavia, with around 3000 graves. Most people were cremated, then mounds of earth were piled over the remains, but some Christian coffins and chambered tombs have been found. The fort and harbour have also been excavated.
In 830 the Benedictine monk Ansgar was sent to Birka by the Holy Roman Emperor to convert the heathen Vikings to Christianity; he hung around for 18 months. A cross to his memory can be seen on top of a nearby hill.
