Alsnö hus

Alsnö hus was a stone castle on Adelsö island beside Lake Mälaren, of which only the foundation ruins remain visible today. The site also features five ancient burial mounds that enhance the archaeological character of the location.

King Magnus III of Sweden built the fortress around 1270 as a strategic administrative center beside the lake. The structure was later destroyed, likely through a medieval attack that left clear traces in the ground.

The site marks where a major royal decree was proclaimed that shaped Swedish society for centuries. Walking through the ruins today, you can sense the importance this location once held for the kingdom's governance and social order.

The site is accessible by bus and cable ferry from Ekerö, followed by a short walk on marked trails. The best visiting conditions occur during warmer months when the paths are dry and easy to navigate.

Excavations from 1916 to 1918 uncovered many crossbow bolts scattered throughout the ruins, suggesting a violent end. These findings indicate the palace likely fell to a deliberate attack rather than simple decay.

Location: Ekerö Municipality

Inception: 1270s

Founders: Magnus III of Sweden

Part of: Birka and Hovgården

GPS coordinates: 59.36056,17.53500

Latest update: December 8, 2025 21:02