Built before 1587, it stands on the left side of St. Peter’s Church, with which it communicates through an interior door. The structure, originally named after Saint Lucy, passed into the hands of the Confraternity of the Holy Cross. The building has a Latin cross plan, with a single nave and covered by a barrel vault. In 1707 the prior of the archconfraternity, the nobleman Don Agostino Carta, had the oratory restored and equipped it with a vault. Further restoration was carried out in 1871 by Rector Delrio, who had the floor restored. During World War II, when the church was occupied by soldiers, some 18th-century furnishings disappeared, particularly the side panels of the high altar depicting scenes from the Passion of Jesus.
