The relics of Saint Leoncius, extracted from the catacombs of Rome with the accompanying jar of blood, were handed over to the Abbot of Solesmes Dom Prosper Guéranger by Pope Gregory XVI on 7 August 1837.
On 4 April 1865, Dom Prosper Guéranger consecrated the high altar at the end of lengthy renovation work at the abbey, and underneath it he built a definitive crypt for the remains of St Leonard.
To this end, he chose to have the crypt decorated with the precious relics in the style of a cubiculum in the catacombs. The relics lay in a kind of arcosolium, with various paintings inspired by those in the Roman catacombs (e.g. a Samaritan woman at the well, a Virgin, a Good Shepherd with his sheep).