Built between 1570 and 1622, when Caltanissetta was opening new urban routes beyond the Aragonese walls, the church staged the civic ambition of a county capital: the classical-style portal, the rusticated pilasters, and the broken pediment introduce an interior with a Latin cross plan of Renaissance design, later enlivened by Baroque taste. Three naves supported by fourteen arches—each once dedicated to a biblical figure—lead to the wide transept topped by an octagonal dome, through which a Mediterranean light filters down onto the polychrome marble floor.
Between 1718 and 1720, the Flemish painter Guglielmo Borremans transformed the central nave into a celestial scenery: trompe-l'œil, architectural wings, and a profusion of angels frame the Immaculate Conception painted on the high altar, while along the vault patriarchs and prophets parade, guiding the faithful in the ascent of the gaze.
In the side chapels, one finds the wooden statue of the Immaculate (1760), draped in repoussé silver garments, and the Crucifix by Fra Umile da Petralia, a sculpture imbued with pathos that, according to tradition, sweated during the plague of the 17th century. Every 29 September, the church becomes the beating heart of the Feast of Saint Michael the Archangel: the precious silver effigy of the patron descends from the altar and parades through the illuminated streets, renewing an identity bond that unites liturgy and folklore.
Bombed in 1943, the cathedral lost its stained-glass windows, later restored in the 1950s together with the stuccoes and the installation of a two-manual organ. From the external staircase, the view embraces the Triton Fountain and the 19th-century fabric of the square, while inside the scent of incense, the dim light of the side aisles, and the shimmering of sacred metals restore to the visitor the suspended atmosphere of a place where international art and popular devotion coexist timelessly, offering a key to understanding the religious and civic history of central Sicily.