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:Rosenborg Palace was built in the period 1606-34 as Christian IV’s summerhouse just outside the ramparts of Copenhagen. Christian IV was very fond of the palace and often stayed at the castle when he resided in Copenhagen, and it was here that he died in 1648. After his death, the palace passed to his son King Frederik III, who together with his queen, Sophie Amalie, carried out several types of modernisation.
The last king who used the place as a residence was Frederik IV, and around 1720, Rosenborg was abandoned in favor of Frederiksborg Palace.Through the 1700s, considerable art treasures were collected at Rosenborg Castle, among other things items from the estates of deceased royalty and from Christiansborg after the fire there in 1794.
Soon the idea of a museum arose, and that was realised in 1833, which is The Royal Danish Collection’s official year of establishment.