Almarestäkets castle was built in the 1100s to protect the Sigtuna and Uppsala cities. It was also called as St. Erik's castle after Eric IX. Throughout the Middle Ages there was a struggle between the Crown and Church who can control the castle.
The castle was first mentioned in the late 1300s. In 1440 got Archbishop Nicolaus Ragvaldi permission to build a new castle, which was completed about ten years later. In the 1510s troubles Almarestäkets was in possession of Bishop Gustav Trolle between 1516-17. The castle was sieged by his main enemy Sten Sture the Younger in 1517. Archbishop Gustav Trolle locked himself in there to avoid trial, and the Swedish government demanded and carried out the demolition of the fortress. The procedure was formally unauthorized because at the time State property was to be separate from Church property. As a revenge for this and other perceived injustices, Trolle, assisted by the Danish King Christian II, took revenge in the Stockholm Bloodbath of 1520.
Today there are visible traces of castle foundations with potholes filled with stone and occasional bricks.
References:The Château de Foix dominates the town of Foix. An important tourist site, it is known as a centre of the Cathars. Built on an older 7th-century fortification, the castle is known from 987. In 1002, it was mentioned in the will of Roger I, Count of Carcassonne, who bequeathed the fortress to his youngest child, Bernard. In effect, the family ruling over the region were installed here which allowed them to control access to the upper Ariège valley and to keep surveillance from this strategic point over the lower land, protected behind impregnable walls.
In 1034, the castle became capital of the County of Foix and played a decisive role in medieval military history. During the two following centuries, the castle was home to Counts with shining personalities who became the soul of the Occitan resistance during the crusade against the Albigensians.