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:The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.