In the heart of Naples, between alchemy and politics, an 18th-century genius created the plot that still fuels devotion today.
I regret having to question one of the cornerstones of the beliefs of a people I love deeply. But, precisely because I love them, I believe it is worth approaching this mystery with a fresh perspective, without detracting from the charm of devotion, but rather adding another possible interpretation: one that leads straight to the Prince of San Severo, Raimondo di Sangro.
In 1757—at a time when the boundary between science, alchemy, and religious ritual was more porous than we imagine today—Naples witnessed the crystallization of a practice that would become a myth: the liquefaction of the blood of San Gennaro. Behind this apparent miracle emerges the ambiguous and brilliant figure of Raimondo di Sangro, Prince of Sansevero, inventor and experimenter on the borderline between empirical experience and esoteric symbolism. The question that arises is simple and disturbing: what if the ‘miracle’ was, in large part, a technical artifact—designed, replicated, and finally handed over to the ecclesiastical power?
Raimondo di Sangro is known today as much for his artistic patronage as for his eccentric experiments. Two key elements emerge from contemporary accounts and modern research: his ability to reproduce materials and phenomena (colored glass, artificial gems, “perpetual light”) and the production of novel objects and technical practices, including the experimental reproduction of blood liquefaction. The Sansevero Chapel Museum and period documentation attest that the prince attempted to reproduce “a certain substance similar to the blood of San Gennaro” through laboratory experiments; his interest in these phenomena caused friction with the Church and aroused the curiosity (and skepticism) of the scientists of the time.
From a chemical-physical point of view, the most plausible modern explanation for the behavior of the ampoules (a substance designed to change from solid to fluid) is thixotropy: a property of certain gels and colloidal suspensions that become more fluid when shaken or heated and then refreeze. This class of materials was consistent with the practical knowledge of 18th-century chemists: mixtures of pigments, metal salts, and gelling agents can be prepared to change appearance when the temperature varies or as a result of vibrations. The thixotropic hypothesis, also supported by CICAP investigations and popular studies, makes it credible that liquefaction could be reproduced artificially.
Why then attribute the phenomenon to a miracle? This is where politics and symbolism come into play. Eighteenth-century Naples was the scene of dynastic clashes and struggles for social influence: a “miracle” that could be reproduced and verified periodically became a powerful tool for cohesion and legitimization. If Raimondo developed a system—ampoules, monstrances, heating or agitation procedures—the Church, custodian of the relic, would have had a clear advantage: a prodigious sign that strengthened popular consent and reinforced moral control. At the same time, the prince would have obtained protection, resources, and a sort of social immunity for his more uncomfortable research. This interpretation does not diminish the faith of the devout, but highlights how techniques and narratives can intertwine to produce symbolic power.
However, there is another, more disturbing shadow that accompanies Raimondo’s name: the so-called ‘anatomical machines’, displayed in the family chapel, which reproduce the venous and arterial circuit with almost miraculous precision. For a long time, popular tradition has told of experiments on living bodies, or post-mortem injections that would have ‘metallised’ the vessels; modern studies indicate, however, that the technique used materials such as wax, metal wires and other handmade compounds, although some details remain shrouded in mystery. For example, the use of red mercury, which has never been confirmed but is possible. What is certain is the symbolic significance of the staging: control of the human body, the ability to imitate nature, and a practice that challenges the moral boundaries of the time.
This picture suggests an overall thesis: it was not so much a single “fraud” as a sophisticated machine of meaning—technical, symbolic, and political—in which the scientist-alchemist and the ecclesiastical institution found a tacit agreement. The former gained protection and resources, the latter a visible sign to govern the collective imagination. And the population? It received a ritual experience that, repeated over time, consolidated into myth and miracle.
An ethical and historiographical question remains: how much of this story is provable and how much remains suggestion? Archival sources, contemporary letters, and the material legacy in the Sansevero Chapel allow us to construct a plausible but not definitive narrative. It is a story that still calls us today to look at the fine line between technical knowledge and symbolic power—and to ask ourselves how much, in history, science has contributed to forging collective beliefs that we now call “miracles.”
Conclusion
The mystery of the blood of San Gennaro loses none of its power, but if we read it as a political-technical project born in the workshop of an eccentric prince, the phenomenon becomes even more fascinating. It is not just faith versus science: it is the story of an unspoken alliance that transformed an experiment into a ritual and an artifice into a miracle.
Main sources consulted
- Sansevero Chapel Museum — information sheets on Raimondo di Sangro and his experiments. Sansevero Chapel Museum — anatomical machines (information sheet)
- CICAP — explanations and hypotheses on liquefaction (thixotropy). cicap.org
- Center for Inquiry / popular articles on the persistence of the phenomenon. centerforinquiry.org
- Study on “The Coronary Tree of the Anatomical Machines” (PMC/NCBI) — modern scientific analyses.
