The Friedberg castle was subsequently built to serve as a border security and customs post for the Duchy of Bavaria and Swabia, but put the town in opposition to the free city of Augsburg. It was built between 1257-1264 by Duke Ludwig II.
The castle was the cause of the first burning of Friedberg by Augsburg in 1396. The town was subject to the many frequent wars between Swabia, Bavaria and Augsburg.
A revival in the town's fortunes came when, in 1568, the Duchess Christine chose Friedberg castle as her seat following her husband's death. The town became the centre of Bavarian court life, but was short lived when the town was ravaged by the plague in 1599. More suffering came as the town was sacked twice by the Swedes during the Thirty Years War. After the war only the town hall, castle and city walls were left standing.
The castle is situated on a spur of and has an unusually deep moat. Since the renovation in 1982, Friedberg castle has been a museum.
Ängsö Castle was first named as "Engsev" in a royal charter by king Canute I of Sweden (r. 1167-1196), in which he stated that he had inherited the property after his father Eric IX of Sweden. Until 1272, it was owned by the Riseberga Abbey, and then taken over by Gregers Birgersson.
From 1475 until 1710, it was owned by the Sparre family. The current castle was built as a fortress by riksråd Bengt Fadersson Sparre in the 1480s. In 1522, Ängsö Castle was taken after a siege by king Gustav Vasa, since its owner, Fadersson's son Knut Bengtsson, sided with Christian II of Denmark. However, in 1538 it was given by the king to Bengtsson's daughter Hillevi Knutsdotter, who was married to Arvid Trolle.
In 1710, the castle was taken over by Carl Piper and Christina Piper. Ängsö Castle was owned by the Piper family from 1710 until 1971, and is now owned by the Westmanna foundation. The castle building itself was made into a museum in 1959 and was made a listed building in 1965. It is currently opened to visitors during the summers.
The castle is a cubical building in four stores made by stone and bricks. The lower parts is preserved from the middle ages. It was redecorated and expanded in the 1630s. The 4th storey as well as the roof is from the expansion of Carl Hårleman from 1740-41. It gained its current appearance in the 1740s.