Miracles are almost by definition unpredictable and spontaneous, except in the Italian city of Naples, where every year the city’s patron saint is believed to keep one of three annual appointments on Sept. 19, his feast day, producing a scientifically inexplicable liquefaction of two ampules of his blood.

On Monday the blood miracle occurred once again, according to Naples’s Cardinal Crescenzio Sepe, who performed the annual ritual of descending into the crypt of the local cathedral to examine the ampules containing what tradition regards as the blood of Saint Januarius, known in Italy as “San Gennaro,” recalled as a martyr during persecutions of the early church under the Roman Emperor Diocletian.

On past occasions, prelates would sometimes bring the still-dry blood in its ampule up to the church, where it would reportedly liquefy before the eyes of the congregation. In this case, however, Sepe announced Monday morning that the blood had already taken liquid form when he went down to take a look.

The announcement was greeted with applause in the cathedral, where the feast of San Gennaro is considered a major civic event.

According to the cult around San Gennaro, his blood was collected by a woman named Eusebia shortly after his death. Devotion to the annual liquefaction, however, isn’t documented until 1389, and over the next few centuries reports circulated about the blood melting up to three times every year: His feast on Sept. 19; Dec. 16, marking his patronage of Naples; and the day before the first Sunday in May, celebrating the reunification of his relics.

The saint’s blood is also believed to liquefy on other special occasions, such as papal visits.

It reportedly did so for Pope Pius IX in 1848, but not for either St. John Paul II or Benedict XVI. When Francis visited in March 2015, Sepe announced that the blood had “half-liquefied.”

Some researchers believe the blood contained in the ampules contains a specific kind of gel that results in viscosity when the ampules are moved or stirred, meaning that there could be a scientific explanation for the phenomenon.

Devotees, however, are convinced the annual events are miraculous, which is why in addition to Naples San Gennaro is also the patron saint of blood donors.

While Church officials obviously support the celebrations in Naples, officially speaking the Vatican has never taken a position on the legitimacy of the miracle, nor has it ever offered a binding theological interpretation for it.

Many devotees of San Gennaro, however, see the liquefaction as a sign of “straining” for the resurrection of the body to come at the Last Judgment.

In addition to the usual civic authorities, beginning with Mayor Luigi de Magistris, this year’s celebration also had an ecumenical flavor. Sepe was joined by an official of the Russian Orthodox Church from Siberia, as well as the head of the local Russian Orthodox community in Naples.

In his homily, Sepe pointedly denounced what he sees as social injustices in Naples, long considered the capital of Italy’s underdeveloped southern region, where youth unemployment rates can reach as high as fifty percent.

“In this city, not everybody can benefit from the same opportunities for social growth,” Sepe said. “The poor are considered only half-citizens, and the lack of work is the cause of both these inequalities and also a grave crisis of legality.”

Naples is also known as a center for Italy’s various forms of mafia activity, and Sepe was blunt in denouncing the grip the mafia often has on civic life.

“Organized crime is the most purulent wound to extirpate, because it infects the body of society that’s already weakened and burdened,” he said, calling organized crime “a continual outrage against our city.”