Glacial erratics have been transported by ice sheets and glaciers, remaining in place when the ice subsequently melted.

Glacial erratics are large rocks that have been transported by ice. It is believed that most of the glacial erratics in Sweden were transported during the most recent ice age. The glacial erratics accompanied ice sheets and glaciers as they advanced over the land. The erratics remained in place when the ice melted, which in the Stockholm region took place around 10,000 years ago. A building of timber and stone known as a “blockhus” was erected here during Gustav Vasa’s reign (Swedish King, 1496–1560) to protect the approach to Stockholm, giving the point its name.