After a miracle was obtained by his prayers, he was discovered and his contemplation interrupted, so he decided to move to another mountain, where he built a beautiful church in honor of Our Lady. His holiness attracted many followers and, in 1119, he established the Congregation of Monte Vergine, or Mount of the Virgin. These sons of Our Lady lived in great poverty. Saint William founded several more monasteries, both for men and women, in various places in the kingdom of Naples. He assisted the king of Naples in practicing all the Christian virtues of a worthy sovereign, and in gratitude, the king had a house of the Order built at Salerno directly across from his palace, to have him near for spiritual advice.
When Saint William died on the June 25, 1142, he had not yet written a Rule for his religious; his second successor, Robert, fearing the dissolution of a community without constitutions, placed them under that of Saint Benedict, and is regarded as the first abbot of the Benedictine Congregation of Monte-Vergine. Although his other foundations did not survive, the monastery at Monte Vergine still exists today.