St Bilo's church is dedicated to a local saint named Bilo, or Beilo, daughter of Brychan. The dedication was recorded as early as the 13th century, but curiously, the church was known for many years as St Milburga's, after the daughter of a 7th century Mercian king and abbess of Wenlock. There must have been a Norman church here, for a reused lintel shows Norman carving motifs, but the building is almost entirely 14th century and later.
The chancel was rebuilt in 1710, and in the 19th century the west end of the church was blocked off and used as a schoolroom. In the south wall is a small window in Early English style, possibly a hermit, or leper window, and in the north wall is a blocked priest's door topped with a lintel carved with a traditional Norman diamond motif, suggesting an 11th-12th century date.
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.