Bulverket

Bulverket - Credit: Wikimedia Commons

The Bulverket is the remnants of a large wooden fortification or bulwark at Lake Tingstäde on the island of Gotland, Sweden. When built, it consisted of a platform with houses surrounded by a double palisade with the entire construction around in diameter. Read more on Wikipedia

type: historic site
date from: 1130

Source: en.wikipedia.org