San Marcello al Corso was built before 418, when Pope Boniface I was elected there. Pope Adrian I, in the 8th century, built a church on the same place, which is currently under the modern church. On 22 May 1519, a fire destroyed the church. The money collected for its rebuilding was used to bribe the landsknechts, who were pillaging the city during the Sack of Rome (1527).
The work was continued by Antonio da Sangallo the Younger, who rebuilt the church, but a Tiber flood damaged it again in 1530. It was only in 1592–1597 that the church was completed with a facade by Carlo Fontana, commissioned by Monsignor Marcantonio Cataldi Boncompagni. The exterior travertine statues were sculpted by Francesco Cavallini, and the stucco bas-relief over the entrance, with depicts San Filippo Benizio, was created by Antonio Raggi.
Under the main altar, decorated with 12th century opus sectile, are the relics of several saints, which include those of Pope Marcellus as well as Digna and Emerita. The last chapel on the left is dedicated to St Philip Benizi. The late-Baroque decoration contains sculptures by Francesco Cavallini and reliefs by Ercole Ferrata and Antonio Raggi. The first chapel on the left has the double tomb of Cardinal Giovanni Michiel and his grandson Antonio Orso sculpted by Jacopo Sansovino.
The church is administered and owned by the Servite Order since 1369.
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.