San Miguel Church is built in the Romanesque to Gothic transitional style, apparent in the combination of elements from both styles inside. The richly ornamental northern front is in the Romanesque style and is considered one of the best in Navarre. The most interesting elements are the reliefs on either side of the front, which represent scenes from the Resurrection and the struggle of the Archangel St. Michael. The interior houses a Gothic reredos painted on stucco. It serves as the grave of the marquis of Muruzábal and Eguía. Of note among the sculptures on the reredos is a 17th century San Crispín.
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.