One is that emperor Constantine I founded the church in gratitude for the rescue of his daughter Costanza from a shipwreck.

Almost razed in 1872, the local canon Giuseppe Perrella commissioned a neoclassical reconstruction, completed in 1887, from engineer George Tomlinson, with help by Errico Alvino and Federico Travaglini.

The major chapel of the Crucifix or Cappellone del Crocifisso, in the left transept, has statues of Costantino and his daughter Costanza sculpted by Lorenzo Vaccaro in 1689.

On the left, in the entry portal for the Oratory of the Confraternity of the 66 priests (Oratorio della Confraternita dei LXVI Sacerdoti) are two tombstones from 999 to 1003, that refer to the foundation and consecration of the basilica.

The chapel of Santa Maria di Costantinopoli (previously known as dei Paleologi) at the left of the nave has a 16th-century fresco depicting Madonna and St Peter.

The Ravaschieri Chapel, dedicated to John the Baptist, was designed and completed by the sculptor Giovanni da Nola.

The first is called the Chapel of the Madonna delle Grazie and has a terracotta presepio (nativity scene) from the 18th century.