San Nicolás church was built in the 12th century not only with religious functions, but also as a defensive bastion of the quarter during the strife with the neighbouring ones of St. Saturnino and Navarrería. The military role is evident in the watch tower. In 1222 the original Romanesque church was destroyed by a fire, and was replaced by a new building, consecrated in 1231.
The interior is in Gothic style, from different phases. It houses a Baroque organ. Exteriorly, of the Gothic period only two portal are visible today, as well as the apse. The corner portico was designed by Angel Goicoechea and built by a local contractor Blas Morte in the 1880s.
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.