The Church of St. Nicholas is an Eastern Orthodox Church in the Bulgarian capital of Sofia. The church was built in the 13th century by Kaloyan the sebastocrator as a small family church on today's Kaloyan Street behind the Rila Hotel. It is assumed that the church was erected on the site of the surviving parts of the palace complex that had once stood there which was built during the Roman Empire and accommodated Constantine the Great. Today these parts are preserved and can be seen in the authentic underground walls of the temple.
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.