In the night of August 23, 1648, as mounted sentinel Antonio Ruffo watched the sea near St. Leonard's Church and the Tower of Cupo, he saw, not the Moslem raiders he was looking out for, but the Holy Virgin, seated over the sea. Arms outstretched, she calmed his fears, calling herself the Madonna of Schiavonea. Afterwards, the watchman commissioned a local artist named Scamardella to paint her portrait, which was carried in procession to St. Leonard's Church on October 13, 1648. Work on a new sanctuary at the site began March 16, 1649. Dedicated to Our Lady of the Snows, after Santa Maria Maggiore in Rome, the shrine and Schiavonea district celebrate their patronal feast day on August 5 with a nautical procession of a standing statue of the Virgin and Child, while the unusual Black Madonna painting remains in the diocesan sanctuary above the main altar. Information from "Apparizione Marina di Schiavonea," mariadinazareth.it. Picture from "Immagini del Santuario di Schiavonea in Santa Maria ad Nives," www.santuari.it.   

Source: http://www.wherewewalked.info/feasts/10-October/10-13.htm