The miracle of San Gennaro: what happens to his blood?

In English he's also known as Saint Januarius, but in Naples he's San Gennaro, and he's much more than a saint: he's almost a neighbour you argue with.

What exactly is the miracle?

The two phials sit inside a silver reliquary which, according to the abbot of the chapel, was commissioned by Robert of Anjou. They're kept in the cathedral, in the chapel that houses San Gennaro's Treasure. Tradition says what they hold is the blood of a martyred bishop who died some seventeen centuries ago.

What everyone is waiting for is the liquefaction: for that dark, solid mass to turn liquid in front of the faithful. When it happens, it's read as the saint's seal of approval on the way his city has behaved.

When does the San Gennaro miracle happen?

Three times a year, on fixed dates: the first Saturday in May, 19 September and 16 December. The September date draws thousands of people.

And if it's late?

Then the anxiety builds. And the saint gets a popular nickname, half affectionate and half reproachful: faccia 'ngialluta, "yellow face", used above all when the wonder keeps everyone waiting.

There was a time when the wait came with a soundtrack, too. A group of women known as San Gennaro's "relatives" would call out to him at the top of their voices, and not exactly politely. Cardinal Corrado Ursi, Archbishop of Naples and very much in tune with what the Second Vatican Council asked of popular devotion, banned those outbursts, because he wanted a serious, reverent atmosphere.

How does Naples feel about its saint?

To understand the miracle, you need to understand that relationship, which is almost one between equals.

In January 1527, with plague, famine and war between France and Spain bearing down, and Vesuvius always next door, the city's representatives signed a notarised vow with San Gennaro at the high altar of the cathedral. The city promised to build him a new chapel; the saint, to protect it from plague, war and the eruptions of Vesuvius. The city kept its word, but took its time: work began in 1608 and the chapel was handed over in 1646.

That chapel is run by a civic board, the Deputazione, which in 2016 went as far as arguing that the saint's treasure is the property of Neapolitans alone, rather than of the Church.

And when, after the Second Vatican Council, a rumour spread that Rome had downgraded the city's saint, Naples answered with a blunt slogan: San Gennà, futtatenne!, roughly "San Gennaro, pay them no mind". The rumour was false: Rome had merely reorganised which patron saints had national or local standing. The slogan, on the other hand, was very real.

How long has the blood been liquefying?

Tradition places the beginning in antiquity. It says a woman called Eusebia collected the martyr's blood on the day he died, and that there was already a liquefaction around the year 420, when his remains were moved.

The written record tells a different timeline. The story of Eusebia first appears in writing in 1579. An earlier Neapolitan chronicle, the Cronaca di Partenope, says nothing about the liquefaction, and a procession in 1337 was recorded with no mention of any wonder. The earliest known written account of a liquefaction is from 17 August 1389, also during a procession, in a Sicilian chronicle, the Chronicon Siculum. We haven't been able to read that chronicle in its original edition, but the sources that cite it agree on the date.

It's worth keeping this in proportion: these dates don't settle whether there's a miracle or not. All they show is when somebody first wrote it down.

Is there a scientific explanation?

There's no proven explanation. What there is, is a set of answers that sit side by side, and none of them has closed the question.

Faith. For believers, it's a wonder worked by the saint. The Church in Naples itself has chosen its words carefully: in Cardinal Ursi's time, the diocese preferred to speak of a "prodigious event" rather than a "miracle".

A disputed analysis. In 1988, a forensic medicine team from Turin announced that spectroscopic analysis had found traces of blood in the phials. That result has been called into question.

A physical hypothesis. In 1991, three Italian researchers, Garlaschelli, Ramaccini and Della Sala, published a proposal in Nature: a mixture made from substances already available in the Middle Ages, which is solid at rest and turns liquid when moved, what's known as a thixotropic substance. They managed to reproduce the effect. But it's a hypothesis about how it might work, not an analysis of what's inside: nobody has tested it by opening the phials. The Pontifical Theological Faculty responded by repeating the experiment in order to refute it.

And a prince who voiced his doubts. Nearly three centuries ago, Raimondo di Sangro, Prince of Sansevero, held a seat on the chapel's board. In one of his books he described the liquefaction as a phenomenon of unknown causes. Note that he didn't call it a trick; he simply admitted that nobody could explain it. A Jesuit reproached him for it, and on 27 December 1752 the nobles gathered in the Sedile di Nido refused to renew his post. The reason? His miscredenza, his lack of faith.

Spot the irony: saying its causes were unknown cost the prince his seat, and two centuries later the diocese itself steered clear of the word "miracle" and preferred to speak of a "prodigious event". In Naples, where San Gennaro is concerned, the nuance is everything.

Fact or legend.

• Fact: the rite exists and is held three days a year; the earliest known written record of a liquefaction is from 1389 (according to the sources that cite it; we haven't read the original chronicle); the notarised vow of 1527; Ursi's ban and his preference for "prodigious event"; the Prince of Sansevero's removal in 1752.
• Tradition: that the phials hold the saint's blood; the story of Eusebia, first written down in 1579; the liquefaction around the year 420.
• Hypothesis and disputed analysis: the thixotropic mixture proposed in 1991 and the traces of blood announced in 1988. Neither has been tested by opening the phials.
• Faith: that it's a miracle. No document can settle that, and we're not taking sides.
• Hoax: the "downgrading" of San Gennaro after the Second Vatican Council.

Where to hear it

The blood of San Gennaro brings the route "Naples: Saints, Skulls and Mysteries" to a close, at the stop "The Blood of San Gennaro", in front of the cathedral's façade. Just before it, "A Contract with a Saint" tells the story of the 1527 vow and the post the Prince of Sansevero lost. Along the way, the route passes the Sansevero Chapel and the church of the adopted skulls, the Purgatorio ad Arco.

If you're planning your trip, our Naples guide has the practical side covered.

Further reading

• Roberto Paura, "Il culto sempreverde della 'faccia ’ngialluta'", Quaderni d'altri tempi, 21 September 2018 (in Italian). https://www.quadernidaltritempi.eu/qdtpdf/6879/
• Franco Capone, "Il potere di San Gennaro", Focus.it, 13 April 2016 (with comments from Vincenzo De Gregorio, abbot of the Chapel of the Treasure; in Italian). https://www.focus.it/cultura/storia/il-potere-di-san-gennaro
• L. Garlaschelli, F. Ramaccini and S. Della Sala, "Working bloody miracles", Nature, 353, p. 507, 10 October 1991 (we've read the article's record page, not the full text). https://www.nature.com/articles/353507a0
• Girolamo Imbruglia, "Sangro, Raimondo di", Dizionario Biografico degli Italiani, vol. 90, Treccani, 2017 (in Italian). https://www.treccani.it/enciclopedia/raimondo-di-sangro_(Dizionario-Biografico)/
• Artribune, "Restauro del pavimento della Cappella del Tesoro di San Gennaro", June 2026 (in Italian). https://www.artribune.com/arti-visive/arte-moderna/2026/06/restauro-pavimento-cappella-tesoro-san-gennaro-napoli/