ROME — While Pope Francis was giving some advice to the religious, priests and seminarians of Naples on Saturday, a miracle occurred: a vial of dried blood from a fourth-century saint liquefied.

This stunning but locally known and accepted phenomenon is said to happen three times a year: May 1, Sept. 19, which is the saint's feast day, and Dec. 16.

The last time this occurred with a pope was in 1848, with Pius IX. It didn't happen when St. John Paul II visited the city in October of 1979 or when Benedict XVI went in October 2007.

The blood belongs to St. Januarius, patron of Naples and former bishop and martyr of the city, whose bones are also preserved in the cathedral. He's believed to have been martyred during the infamous persecution of Christians during the rule of Roman Emperor Diocletian, who retired in 305.

On March 21, at the end of the meeting with priests, religious and seminarians in the cathedral of Naples, the Pope gave a blessing with the relic. When received by the cardinal of the diocese, Crescenzio Sepe, the blood was solid on only one side of the vial.

When Pope Francis returned the reliquary, the cardinal told him: “It seems that St. Januarius loves the Pope, because the blood is already half liquefied.”

For the miracle to occur, it's necessary to wait several minutes before the dried, red-colored mass confined to one side of the reliquary becomes blood that covers the entire glass.

Francis quipped in response: “You can see that the saint only loves us a little. We have to convert more,” drawing laughter from those within earshot.