The various phases of construction and reconstruction, which over time were added to the original structure, justify different stylistic overlaps.
The Cathedral in the 14th century extended the three naves with a succession of octagonal columns topped by pointed arches, as seen today along the southern nave.
The Cathedral consisted of three naves, a transept with three apses. The main tribune was dedicated to the Virgin Assumed into Heaven and Saint James, the second right tribune to Saint Gerlando and Saint John the Evangelist, and the third to the north in honor of Saint Stephen the Protomartyr and Saint Giles the Abbot. This seems to be the extension of the church in the first half of the 14th century, corresponding to the current one.
Following are the altar of Saint Eligius, the altar of the Sepulcher of Saint Gerlando, the chapel of Saint Bartholomew, the altar of Saint Mary, and the altar of Saint Agatha. The roof was probably characterized by a truss ceiling, of which no trace remains.
Between 1330 and 1360, the Cathedral expanded the arrangement of the naves, now identified in the succession of octagonal sandstone pillars, today remaining only along the southern side of the central nave of the church, and a series of empty lunettes that were once finely frescoed, thanks to the financial contribution of noble families from Agrigento.
Originally, two marble sarcophagi were meant to hold the bodies of Markisia Prefolio, a noblewoman from Agrigento, wife of Federico Chiaramonte, and their son Federico, as well as Marino Capizzi.
From this period date the frescoes of the southern nave and the chapel of Saint Bartholomew under the Norman clock tower. The frescoes detached in 1951 are now kept in the Diocesan Museum halls. These are thirteen fragments, dating between the 14th and 15th centuries.
Along the southern nave, a series of arcosolia housed other frescoes. The lunette, now closed, near the current chapel of Saint Gerlando, was decorated with the Ascension and a figure of a Saint on the Throne; in the second, a triptych depicting the Madonna with Child between Saint Onuphrius and the Madonna with Child, and in the reveals two figures of Saints; in the third lunette, Saint Dionysius of France; in the fourth, Saint John the Evangelist; and the Madonna of Itria placed on one of the pillars, in front of the chapel of Saint Bartholomew.
The chapel of Saint Bartholomew today preserves, at the lower level, a vaulted chapel dedicated in the 14th century to Saint Bartholomew, with traces of frescoes depicting Saint Bartholomew, the Crucifixion and the Madonna del Latte, Saint Christopher, and a Saint, which are now musealized.
