Alphonse Marie Ratisbonne (1814–84) belonged to a prominent Strasbourg Jewish banking family: a free-thinker, twenty-seven years old and engaged to be married, visiting Rome for the first time in January 1842 on his way to Naples. Baron Théodore de Bussières, a recent Catholic convert, wagered him that he would wear a Miraculous Medal (the medal of the Rue du Bac, struck since 1832) and pray the Memorare of St. Bernard once a day. Ratisbonne agreed, treating the whole affair as a joke.
On 20 January 1842, accompanying de Bussières on errands in central Rome, Ratisbonne went into the church of Sant'Andrea delle Fratte to wait while his friend conferred with a priest about funeral arrangements. Alone in the church for a few minutes, he suddenly saw — in the side chapel of the north transept — the Blessed Virgin in the precise pose of the Miraculous Medal: standing on a globe, hands outstretched, rays of light streaming from her palms. She did not speak; the apparition lasted only seconds. When de Bussières returned he found Ratisbonne on his knees, weeping, his hand pressed to the medal beneath his shirt, repeating: 'I have seen her — she said nothing, but I understood everything.'
He was baptised eleven days later, on 31 January 1842, by Cardinal Costantino Patrizi, taking the name Marie-Alphonse. On 3 June 1842, after depositions from twelve witnesses — among them his elder brother Fr. Théodore Ratisbonne, already a Catholic priest — the Vicariate of Rome declared the apparition 'a true and manifest miracle wrought by God most holy and glorious'; Pope Gregory XVI received Ratisbonne's testimony personally. He broke off his engagement, became a Jesuit, was ordained priest in 1848, and left the Jesuits in 1852 to found with his brother the Congregation of Our Lady of Sion, dedicated to the conversion of the Jewish people and to Jewish–Christian friendship. He spent the rest of his life in the Holy Land, dying at Ein Karem near Jerusalem in 1884. The chapel of the apparition at Sant'Andrea delle Fratte is marked by a marble plaque and a copy of the Miraculous Medal set into the floor.