First mentioned in 431, the church was rebuilt in 439 by Sixtus III with backing from Emperor Valentian III's wife Eudoxia, and dedicated to Saints Peter and Paul. In 442 Eudoxia gave Pope Leo I the chains that had held Peter in prison in Jerusalem; he put them together with the chains that had bound the saint at the Carcere Mamertino (Mamertine Prison), whereupon they miraculously fused. It was only in the 11th century, however, that Gregory VII changed the dedication to St Peter ad vinculum - in chains. The church was repaired in the 15th century, and then modified and restored in the 19th.
The chains are in a reliquary beneath the high altar and are the objective of the pilgrims who flock to the church. Secular tourists head for the funerary monument of Pope Julius II with Michelangelo's imposing Moses (c1513) as its central figure. Julius had wanted an enormous sepulchre with 40 life-size statues in a vast free-standing architectural framework. The proposed scale of the tomb was one of the reasons for the rebuilding of St Peter's, but it quickly became clear that neither the tomb nor the basilica would be finished before the sickly pope expired. So Julius shifted Michelangelo to work on another pet project: redecorating the cracked ceiling in the Sistine Chapel.
After the completion of the ceiling Michelangelo went back to work on the tomb, but seven months later syphilis got the better of Julius and the tomb was put on a back-burner. This considerably abbreviated version was cobbled together by Michelangelo's pupils. The magnificent Moses (horned, from an archaic mistranslation of an Old Testament phrase really meaning 'with light emanating from his head') dominates the composition. The master's hand can be seen in the statues of Leah and Rachel to either side of the patriarch. After a recent restoration, experts came to the conclusion that he may have carved the pope's head too, although he clearly had nothing to do with the rest of poor Julius, which is by Maso del Bosco. When completed, the monument was placed here where Julius had been titular cardinal. His body ended up in an unmarked grave across the river in the Vatican.