Alsnö hus

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Alsnö hus is the ruined palace at the Hovgården archaeological site on the island of Adelsö in Lake Mälaren, central-eastern Sweden. It is part of the UNESCO World Heritage Site Birka and Hovgården. The ruin is next to five large burial mounds from the Vendel Period (roughly 500–800 AD), when Hovgården was a king’s court.

The palace shows how important Birka, the trading town on nearby Björkö island, was. Birka was abandoned around 975, but the royal mansion stayed important, as shown by the runestone U 11 erected beside it around 1070. Alsnö hus is first mentioned in 1200 as a large royal house.

About 70 years later, King Magnus Barnlock replaced the old fortress with a brick summer residence. This building was meant for comfort, not defense, and it was used by Magnus and his son Birger during summers. In 1279 the Ordinance of Alsnö was issued here, and it is often seen as the start of the Swedish nobility as a separate social class and the beginning of the Swedish feudal system.

Large parts of the nearby Adelsö Church date from this period and may have been commissioned by the king. The building fell into ruin by the end of the 14th century. When archaeologists excavated the site in 1916–1918, they found many crossbow bolts, suggesting the palace might have been burned by pirates led by Albert von Mecklenburg, who raided the Baltic to try to restore Albert to the Swedish crown.

In the 1950s–60s the ruins were bought by the Royal Swedish Academy of Letters, History and Antiquities and are now preserved by the Swedish National Heritage Board.