open: according to the church website San Marcello is open from 7am until midnight daily, Saturday 9:30-24:00, July/August 8:30-24:00
San Marcello al Corso was built in the 16th century on the site of an earlier church destroyed by fire in 1519. All that survived the fire miraculously was a wooden crucifix, now in the Chapel of the Crucifix. The church was dedicated to Pope Marcellus I, the church's patron saint (the original church was built in the 5th century over what was thought to have been his prison).
During the Sack of Rome in 1527 decoration of the church was abandoned. In the fourth chapel are frescoes begun by Perino del Vaga but left unfinished. These frescoes were later completed by Daniele da Volterra.
In the first chapel on the right is the Annunciation by Lazzaro Baldi.