Alsnö hus located on terrain feature Adelsö
Alsnö hus (Alsnö House) is the ruin of a palace at the Hovgården settlement archaeological site, located on the island of Adelsö (formerly called Alsnö) in Lake Mälaren in central-eastern Sweden. The ruins are part of the combined Birka and Hovgården UNESCO World Heritage Site.History
The ruin is next to five burial mounds, up to 45 meters in diameter, which date back to the Vendel Period (i.e. Late Iron Age, c. 500-800 AD) when Hovgården was a King's Court (Kungsgård).  The royal castle Alsnö hus reflects the importance of Birka, the trade settlement on Björkö island just south of Adelsö.  However, Birka was abandoned around 975, but apparently the royal mansion continued to be of importance as the runestone U 11 (c. 1070 CE) was erected next to it.