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
Roman temples, along with a jail (carcer) which a tradition (supported by
Pliny's history of Rome) states was sited in the temples' ruins. However, the
in Carcere (in jail) 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 (LPD i.515, n13; ii.295, n12).
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 frontal 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 northern wall of the church. Six columns from the
Temple of Spes are visible in the southern wall. The dedication to
Saint 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 (though the medieval
campanile - originally a fortified tower, then adapted to a bell tower after being abandoned - was not altered). 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
basalt bath tub containing martyrs' relics. ==Present==