The first church on the site was probably built in the 6th century, and a 10th-century inscription may be seen on a fluted column next to the entrance, but the first definite dedication is from a plaque on the church dating to 1128. The inscriptions found in S. Angelo, a valuable source illustrating the history of the Basilica, have been collected and published by Vincenzo Forcella. It was constructed in and from the ruins of the Forum Holitorium and its temples, along with a jail which a tradition states was sited in the temples' ruins. However, the in Carcere part of the name of the church was only changed to "in Carcere Tulliano" in the 14th century, owing to an erroneous identification. The prison was really that of Byzantine times. Spolia from all these ancient remains is still apparent in the church's construction, most particularly three columns from the Temple of Juno Sospita which are incorporated into both the 10th century and 1599 north façades of the church. The columns of the Temple of Janus, dedicated by Gaius Duilius after his naval victory at the Battle of Mylae in 260 BC, can still be seen as being incorporated into the wall of the church. The dedication to St Nicholas was made by the Greek population in the area. In the 11th century, it was known as the church of Petrus Leonis, referring to the converted Jewish family, the Pierleoni, who rebuilt the nearby Theatre of Marcellus as a fortress. One of their members, Pietro Pierleone, was an important cardinal in the 1120s and was elected Pope Anacletus II, though he was later branded a schismatic antipope. The church was rebuilt in 1599, with a new facade by Giacomo della Porta. Stairs under the altar lead to the crypt and to the base of the former Roman temples. Beneath the high altar is also an ancient basaltbath tub containing martyrs' relics.
Present
The church is known for celebrations to the devotion of the Madonna; one is the Italian Our Lady of Pompeii, whose feast is celebrated here, and the other is the Mexican Our Lady of Guadalupe, a reproduction of whose miraculous painting, sent here from Mexico in 1773, is shown.
