In a quiet corner of Hadrian’s Villa, wedged between the so-called Amphitheater and a low platform of volcanic tuff, stands a marble slab measuring approximately 40 by 35 centimeters. It has not been moved for about 1,900 years.
Two lines of carved capital letters explain why archaeologists are so excited: FVLGVR SVBMANIVM—”lightning of Summanus.” Summanus was the Roman god worshipped when the heavens opened at night.
A team of researchers from the Department of Humanities (DISTUM) at the University of Urbino Carlo Bo—conducting excavations with the permission of the Italian Ministry of Culture and in collaboration with the Institute of Hadrian’s Villa and Villa d’Este—discovered something that almost never survives intact: a religious inscription still located at the very spot for which it was carved, undisturbed since ancient times.
The slab is embedded in the front of a small square structure made of tuff blocks and mortar—built, according to the researchers, precisely where a lightning bolt struck the ground. This structure may mark a bidental: a sacred enclosure used by Romans to protect a site sanctified by the divine.
It is worth explaining why a lightning strike warranted the creation of such a monument. In Roman religion, not all lightning bolts came from the same god. Daytime lightning belonged to Jupiter, ruler of the sky. Nighttime lightning belonged to Summanus—a deity largely forgotten today but who, according to ancient sources, had his own temple near the Circus Maximus in Rome. After a lightning strike—regardless of which god had sent it—the ground it hit ceased to be ordinary. It became sacred: set apart and placed under divine protection. Walking on it, plowing it, or building upon it without the proper ritual was considered an affront to the gods.
This practice had a name: fulgur conditum, or “buried lightning.” Priests would gather whatever the lightning had scorched or struck, place it in a pit along with offerings, recite ritual formulas, and then seal the site with a small monument.
The Roman poet Lucan depicted this scene in Pharsalia through the figure of the Etruscan soothsayer Arruns, who was preparing for a lightning strike on Pompey’s military camp: he gathers the scattered embers, buries them in the ground while reciting prayers, and thereby restores the land’s sacred status—before sacrificing an animal on that very spot (Lucan, Pharsalia, I.606–608). The Roman grammarian Festus provided a legal definition: land struck by celestial fire was termed fulguritum—land that a god had claimed as his own.
These enclosures—known as bidentalia, named after the two-year-old sheep (bidens) believed to be sacrificed during the rite—were not tended by ordinary priests. The ceremony was performed by specialized bidental priests, and the practice itself was adopted from the Etruscans, who were considered experts in interpreting lightning—a discipline known as disciplina fulguralis.
Rome adopted this custom during the Republic and spread it throughout the empire. Similar inscriptions on bidentes or fulgura have been discovered in Pompeii, Vulci, Todi, Minturnae, and—notably—in southern Gaul (modern-day southern France), where evidence outside Italy is most abundant.
What makes the discovery at Hadrian’s Villa unusual is the context. Most fulgur finds consist merely of a pit or enclosure lacking an inscription—or an inscription that was reused in a later building, stripped of its original context. Here, however, the slab remains embedded in the very structure built to house it, allowing researchers to examine the entire picture: the ritual act, the monument marking it, and the surrounding landscape.
According to an official statement from the Ministry of Culture, the discovery was made in the area between the amphitheater and the tufa embankment, where archaeologists uncovered a small, square structure made of mortar-bonded tufa blocks, with the inscribed slab still set into its face.
This discovery follows another find linked to the fulgur conditum ritual that garnered international attention: the bronze artifacts from San Casciano dei Bagni in Tuscany, where excavations in 2022 revealed an Etruscan-Roman thermal sanctuary containing 24 remarkably …well-preserved bronze statues. Among the items discovered was a bronze lightning-strike marker lying next to a flint arrowhead—a pairing that archaeologists also link to the fulgur conditum ritual.
Italian Minister of Culture Alessandro Giuli personally visited Hadrian’s Villa following the announcement of the find. He drew a direct parallel with a Tuscan precedent, describing the new discovery as a significant addition to our understanding of one of Italy’s most important archaeological sites—a rare, tangible testament to how Romans perceived land touched by the divine. Alberto Samonà, Director of the Institute of Hadrian’s Villa and Villa d’Este, noted that the discovery shifts the focus from grand architecture to the more intimate side of Roman religious life, offering a direct glimpse into the meticulous ritual procedures of the era. He commended the excavation leader, Fabio Giorgio Cavallero, and the team from the University of Urbino—who worked alongside the Institute’s own archaeologists—for the discovery.
For readers unfamiliar with the site: Hadrian’s Villa is located in Tivoli, approximately 28 kilometers east of Rome. Emperor Hadrian built it between 118 and 138 AD, spanning an area of about 120 hectares—a vast complex of palaces, baths, gardens, theaters, and ceremonial spaces inspired by locations he visited during his travels across the Roman Empire. For comparison, this area is larger than New York’s Central Park.
UNESCO designated it a World Heritage Site in 1999. Today, only about a third of the original grounds—approximately 40 hectares—is open to visitors. The Amphitheater sector, where the inscribed slab was discovered, had already attracted attention in 2024 when archaeologists excavated a palace that had been deliberately demolished and buried beneath later structures.
For this reason, the discovery raises more questions than it answers. Excavation director Fabio Giorgio Cavallero notes that the stratigraphic relationship between the fulgur structure and the remains of the earlier palace could help reconstruct the full sequence of changes this part of the villa underwent over the centuries.
It has not yet been confirmed whether this small tuff structure is a fulgur in the strict technical sense or if it served a related yet distinct function within the same ritual tradition. Nor has its precise date of construction been established relative to other building phases at the site. The team from Urbino plans to continue refining this chronology in future excavation seasons, while the Institute of Villa Adriana and Villa d’Este prepares for new fieldwork in other areas of the site in the coming months.
About the Author
