The Cathedral Church of Saint German was built in 1879–84. The Patron of the Cathedral, St German of Man, was a Celtic missionary and holy man who lived from about 410 to 474.
The original cathedral of St German was inside the walls of Peel Castle and was built sometime in the 12th century when St Patrick's Isle was in the possession of Norse kings. At that time the church followed the Sarum Rite, prevalent throughout much of the British Isles. Around 1333 the Lords of Man refortified St Patrick’s Island and occupied the church as a fortress. In 1392 William Le Scroop repaired the Cathedral.
The building fell into ruin in the 18th century. After a considerable period of debate over who owned the ruins and site, it was decided not to rebuild that cathedral. The present building was constructed in 1879–84 to replace St Peter's Church in Peel's market place. In 1895, the bishop consecrated his chapel at the bishop's palace as pro-cathedral and instituted a chapter of canons with himself as Dean. That arrangement (bishop as dean) persisted even after the consecration of the new cathedral.
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.