The convent and church of St. Clare was founded on the site in 1280s. It was to be one of the very first convents to be dissolved during the Swedish Reformation. Gustav Vasa had the church and convent torn down in 1527.
The new Lutheran church, built under the order of King John III in 1572, is a cruciform shaped. It has the second highest tower in Scandinavia, over one hundred metres high. The interior contains a fine altarpiece and pulpit, both made in the mid-18th century.
References:Sigmaringen Castle was first mentioned in the year 1077 in the chronicles of Petershausen monastery. The oldest parts of the castle are concealed beneath the alterations made during the 17th and the 19th centuries. The secret of the earliest settlement built on this defendable rock will never be fully revealed: large-scale excavation work would be necessary, which the extensive land development renders impossible. Judging from the many Roman remains unearthed in the area around Sigmaringen, the 12th century keep known as the 'Roman Tower' could be traced back to a Roman predecessor.
The castle remains that have been preserved (gate, great hall and keep) date back to the Staufer period around 1200. The castle remains were integrated into subsequent buildings. The foundations of the castle buildings are to a large extent identical to the surrounding castle wall.
These remains give us a good idea of how the castle might have looked during the 12th century.