On November 27, 1830, the Most Blessed Virgin Mary appeared to a young Sister of Charity in Paris at the rue du Bac. She ordered her to have a medal made representing the image she showed her. St. Catherine Labouré, in religion Sister Catherine of Charity, did so.
It was an image of the Immaculate Mother of God showering down heavenly graces from her open hands and crushing the head of the serpent under her feet. The invocation “O Mary conceived without sin, pray for us who have recourse to thee” surrounds the image.
On the back of the medal is the Cross of Calvary intertwined with an M for Mary, along with twelve stars and the most pure hearts of Jesus and Mary.
The medal was soon made, and millions were distributed. It very quickly came to be called the Miraculous Medal because of the extraordinary conversions and favors obtained through it.
In 1839, Pope Gregory XVI authorized a feast of the Immaculate Conception in the diocese of Paris after the apparitions of the rue du Bac. In 1854, Pope St. Pius IX defined the dogma of the Immaculate Conception.