The Romanesque Mother Church of San Leone Magno is where the inhabitants of Castellana founded the town for the third time, after Castellano Vetere and Castellano Novo.
The church is divided into three naves and preserves baroque ornamentation, such as the chapel of the Blessed Sacrament.
You can admire some statues by Aurelio Persio (1518-1593) and 18th century paintings of the Neapolitan school by the artists Miglionico, Ruoppolo and Vincenzo Fato, such as Madonna con Bambino tra i Santi Vescovi Donato e Biagio.
The exterior of church stands in all its grandeur and is dominated by the bell tower, built on the rudimentary Norman defence tower.