A rare megalography from the first century BC has just been uncovered in Pompeii, a site that never ceases to reveal extraordinary finds. A few kilometers to the north, in Pozzuoli, the Macellum — commonly misidentified as the Temple of Serapis — is once again proving its importance, serving as an open-air laboratory for scientists studying the movement of the Earth’s crust. Archaeology certainly helps preserving art and history but it also provides valuable insights into natural phenomena.
In recent weeks, earthquakes have become more frequent in the northern districts of Naples. The second week of March brought the strongest tremor in forty years, following the May 20, 2024, earthquake. With a magnitude of 4.4, it caused significant damage in Bagnoli. According to the National Institute of Geophysics and Volcanology, this event — accompanied by an extended earthquake swarm — is linked to the increasing rate of ground uplift, which in recent months has accelerated from 0.39 to 1.18 inches per month. This phenomenon, known as bradyseism, is a cycle of slow ground subsidence followed by more rapid uplift, typically accompanied by low-magnitude, shallow earthquakes. Over the past twenty years, the ground in this area has risen by 55 inches.
Arriving in Naples, the imposing silhouette of Mount Vesuvius dominates the horizon. Visiting the spectacular ruins of Herculaneum, Stabiae, and Pompeii, one cannot help but feel the unsettling proximity of the volcano, which in 79 AD buried Pompeii under a thick layer of ash and pumice, preserving the city in a frozen moment of destruction and history. While the excavations continue to reveal extraordinary finds — most recently a magnificent megalography in deep Pompeian red — few people notice the immense semicircle that defines the coastline of Naples.
This natural formation is, in fact, the caldera of an ancient supervolcano, which erupted approximately 100,000 years ago, during the Late Pleistocene, in what was one of the most powerful eruptions in the area’s geological history. Confirmation of this came from a recent study published in Nature – Communications Earth and Environment, conducted by researchers from the Institute of Environmental Geology and Geoengineering (CNR), the National Institute of Geophysics and Volcanology, and the universities of Sapienza (Rome) and Aldo Moro (Bari).
These findings offer further evidence of the region’s complex and active volcanic system, highlighting the fact that Naples and its surroundings rest on one of the most geologically dynamic areas on the planet.
Today, the active caldera reveals itself through the fumaroles of the Solfatara in Pozzuoli and the ongoing effects of bradyseism, the same phenomenon that, in antiquity, led to the gradual submersion of Baiae. This once-glorious Roman seaside town, renowned for its luxurious villas and thermal baths, is now one of the world’s most fascinating underwater archaeological sites. Beneath the sand lie paved streets, houses, mosaics, and statues, even the Nymphaeum of Emperor Claudius, all preserved in a submerged world now inhabited by fish and algae.
The Phlegraean Fields — whose name comes from the Greek for “burning land”—continue to rise and fall, creating significant challenges for the local population. Imagine a pot of water on the verge of boiling — this is what happens beneath a densely populated area home to half a million people.
This is where the Macellum comes into play. With its three cipollino marble columns, this archaeological site is not only a symbol of ancient Puteoli — modern Pozzuoli — but also a scientific marker of bradyseism in the Phlegraean Fields. The structure, now standing along the marina, was once completely submerged. We know this because of the holes left by marine mollusks on its walls and columns, which have allowed researchers to track the rise and fall of the ground over the past two thousand years.
Discovered in 1750 but dating back to the 1st or 2nd century AD, the Macellum is an extraordinary witness to geological change, located almost at the precise center of the Phlegraean volcanic caldera. It offers visible proof of how the earth has repeatedly risen and sunk over the centuries. At one point, the ground dropped so dramatically that the sea flooded the area, submerging the site entirely. Slowly, it began to re-emerge, until it appeared much as we see it today. By dating the boreholes of lithodomus mollusks, scientists have been able to trace the vertical movement of the land over time.
When the Macellum was originally built, its columns stood above sea level, but between the 4th and 5th centuries AD, bradyseismic subsidence caused them to sink below the waterline. The land began to rise again in the 13th century, when the columns were more than 26 feet (8 meters) underwater, and by 1538, the Temple of Serapis had re-emerged, lifting nearly 20 feet (6 meters) above the sea. The descent resumed in the mid-19th century, once again submerging the site beneath the waves.
The most recent phase of ground uplift, which has allowed us to see the Macellum as it stands today, began in 1982-1984. Up and down, as if the volcano beneath it were breathing. Just a few kilometers away, another masterpiece has resurfaced in Pompeii, almost contemporary to the Macellum in its origins. More than a century after the discovery of the spectacular Villa of the Mysteries, this latest find sheds new light on the mysteries of Dionysus in the classical world.
In a grand banqueting hall, excavated in Insula 10 of Region IX, archaeologists have uncovered a megalography — from the Greek “large painting” — that spans three walls, while the fourth side opened onto a garden. This newly discovered fresco, now known as the Frieze of the House of the Thiasos, depicts a procession honoring Dionysus, god of wine and revelry. The scene is alive with Bacchantes, portrayed both as graceful dancers and fierce huntresses, alongside young satyrs playing the double flute. At the center stands a woman on the brink of initiation into the mysteries of Dionysus, a deity who dies and is reborn, offering his followers the promise of the same fate.
In antiquity, mystery cults such as that of Dionysus were exclusive and secretive, open only to those who underwent an initiation ritual. The term “mystery” derives from this secrecy—only initiates were allowed to learn the rites and doctrines. These cults often revolved around the promise of a blessed existence, both in this life and in the afterlife.
A fascinating detail in these frescoes is that all the figures stand on pedestals, resembling statues, yet their postures, skin tones, and garments make them appear strikingly lifelike. “Behind these extraordinary paintings, with their interplay of illusion and reality, we see the signs of a religious crisis sweeping through the ancient world,” explains Gabriel Zuchtriegel, director of the Archaeological Park of Pompeii. “At the same time, we glimpse the grandeur of an ancient ritual tradition — one that dates back to the second millennium BC, to the Dionysus of Mycenaean and Minoan cultures, where he was also known as Zagreus, lord of wild animals.”
The newly discovered Pompeii frieze has been dated to 40-30 BC, meaning that by the time Vesuvius erupted in 79 AD, it was already a century old. The only other comparable megalography featuring Dionysian rituals is the famous frieze of the Villa of the Mysteries, a must-see in the vast archaeological park. The Dionysian Thiasos Hall, however, is the latest revelation — and is already open for viewing by appointment.
Excavations in Region IX, one of Pompeii’s nine districts, began in February 2023, covering an area of 3,200 square meters — nearly an entire city block of the ancient site. The dig has revealed two atrium houses, originally Samnite-era residences, which were later converted into productive workshops in the 1st century AD: one was a fullonica (laundry), and the other a bakery, complete with a furnace, millstones, and spaces for food processing. To the south of these former house-workshops, archaeologists have brought to light a series of residential quarters, including a grand domus. Among the most remarkable spaces is the banquet hall decorated with Dionysian scenes, a striking memento of the mystery cults of the time. Another significant discovery is a black salon, where episodes from the Trojan War unfold across the walls, adding yet another layer to the cultural and artistic wealth of the site. Close by, a blue sanctuary has emerged, its frescoes depicting the four seasons, along with allegories of agriculture and pastoral life. Further exploration has also revealed an extensive bath complex, a discovery that offers new insights into the daily life and social customs of Pompeii’s élite.
Still awaiting excavation are the main entrance, the atrium quarters, and a large section of the peristyle garden, areas that could provide even more details about the layout and function of the house. In total, archaeologists have identified more than 50 rooms, covering 1,500 square meters — a discovery that continues to expand our understanding of the city’s architectural evolution.
With so much already uncovered, and even more waiting beneath the surface, the next phase of excavations promises to be just as extraordinary.
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