Integrative Natural History of the Phlegrean Fields, Part 1: Welcome to the Macellum | Pozzuoli, Campania, Italy

Introductory Note: This new series is a follow-on to my my Integrative Natural History of Mount Vesuvius & the Gulf of Naples album, which includes views of the Phlegrean Fields (Campi Flegrei) region from seaward. It also discusses the local geology at length.

In this follow-on album I’ll present additional information from much closer and decidedly more terrestrial vantagepoints. The main sites to be covered are the Macellum of Pozzuoli, that town’s Solfatara maar, and ancient Cumae. But I may also wander farther afield in Campania.

- - - - - -

Facing northeastward, with my back to the Gulf of Pozzuoli and the adjacent harbor. The lack of good horizontal sight lines and true verticals is due to the slanting roadway and embankment behind this archaeological site, and to the various orientations of its ancient columns.

The fact that I took these photos late on an autumn afternoon, with slanting low-level light, also adds to the unsettling effect. As does the reflecting surface of the water. That water is no longer there, but in 1975 the ground surface was almost 2 m / 2.2 yd lower than it is now. And that put it below sea level.

I first became aware of this famous site when I was a university student and came across the famous illustration and explication of it in Charles Lyell’s Principles of Geology. When I actually visited the place four years later, I felt like a pilgrim finally reaching a holy shrine.

For a very long time this set of ruins was misidentified as the Temple of Serapis, or Serapeum. Since the beginning of the twentieth century, however, archaeologists have realized that it as a macellum, or market center. It was constructed by the Romans either in the Flavian dynasty, late in the first century AD, or early in the second under succeeding emperors. And later it was rebuilt or at least spruced up in the time of the Severans, in the early third century.

The most geologically notable feature of the Macellum is found in its three tallest columns, which once supported the portico of the market’s exedra. As photos of following posts will more clearly show, these marble shafts have darkened, eroded zones about one-third of the way up from the water lines. These contain many boreholes made by the marine mussel Lithophaga lithophaga. Other stone-drilling mollusks are also present in the Gulf of Pozzuoli, and may have also contributed.

Lithophaga is a particularly apt name; it means “rock eater.” The mussel excavates, apparently primarily by chemical secretions that dissolve calcite found in limestone and marble, a tidy little chamber in which it passes the rest of its existence.

Borings on columns that were obviously once submerged but are now exposed to the open air suggest that sea level has lowered dramatically over the years. And this has provoked the speculations of a bevy of geologists and naturalists, including Johann Wolfgang von Goethe. That great German polymath came up with a highly imaginative hypothesis that was both worthy of his lofty poetic imagination and quite thoroughly wrong.

But Lyell was one of those who correctly posited that the relatively gentle vertical motion of the land itself was responsible for the exposure of the mussel holes so high above the water’s current surface. In fact, he made the case for the process now known as bradyseism, the gradual rise or fall of the Earth’s surface. After all, really powerful earthquakes generating rapid movement would probably have caused the columns to topple long ago.

Since Lyell’s time in the nineteenth century, other geologists have noted that this site lies close to the center of the Phlegrean Fields caldera complex, a collection of nested volcanos that have erupted and then collapsed at different times in the Pleistocene and Holocene. That in turn implies a lot of magmatic activity underground.

In fact, it’s now thought that beneath this complex lie two magma chambers—a lower, larger one about 7.5 km / 4.7 mi deep, and the upper, smaller one at 3 km / 1.9 mi below the surface. Many vulcanologists contend that it’s the second of these, alternately fed or drained by the first, that causes the crust under Pozzuoli to swell and then sink again.

When I took this photo fifty years ago, the Macellum and its surroundings were on their way up, but they were not yet high enough to fully drain off the seawater. From what I’m able to gather, total emergence didn’t occur until almost a decade later.

While the research literature on bradyseism and for that matter on stone-excavating bivalves is by no means wanting, there has apparently been no attention given to the Macellum by architectural geologists or petrologists. References to the stone types present here are frustratingly vague and poorly documented, if documented at all. But this is what I have been able to piece together so far. Note that all the following identifications are tentative.

- Of the site’s many columns, the three discussed above are clearly marble of the generic type known as “Cipollino.” In recent times, “Cipollino” varieties have been marketed by marble quarriers from Vermont to Carrara and beyond. But rock of this description produced in the Imperial Roman era was almost always Karystos Marble, from the Greek island of Euboea.

- The circular tholos structure in front of the tall portico columns has the stubby remains of sixteen columns reportedly made of “African Marble” or “Numidian Marble.” This probably equates to Numidian Yellow Breccia, from what nowadays is Chemtou, Tunisia. It’s not a true marble, but that fact never restrains archaeologists or architectural historians from calling it that.

- There were also thirty-four columns of “gray granite” that supported the market’s arcade of shops. If it really is a granitoid, my best guess is that it came from the Tuscan islands of Giglio or Elba, or that it’s Aswan Granodiorite from eastern Egypt. The Romans used all of these at different times.

So it’s obvious that the Macellum, not to mention the Phlegrean Fields in general, can provide much grist for my mill. All these things and much else will be discussed further in posts to come!

Primary Sources for this Essay

- Ricci, Sandra, Carlotta Sacco Perasso, Federica Antonelli, and Barbara Davidde Petriaggi. “Marine Bivalves Colonizing Roman Artefacts Recovered in the Gulf of Pozzuoli and in the Blue Grotto in Capri (Naples, Italy): Boring and Nestling Species.” International Biodeterioration & Biodegradation 98 (2015): 89-100.

- Bellucci Sessa, E. and G. Milano. “Ground Uplift and Seismic Activity at Campi Flegrei Caldera (South Italy) during the Unrest Episodes: An Overview.” Bulletin of Geophysics and Oceanography 20:10 (2024).

Taken in: Italy / Campania / Pozzuoli (show map)

Taken on: November 9, 1975

Tags:

archaeology

architectural_geology

geology

landscape

rock

rocks

stone

stonework

Italia

Italy

Pozzuoli

Macellum

Temple of Serapis

Serapeum

bradyseism

mollusk borings

tholos

columns

Numidian Yellow Breccia

Karystos Marble

cipollino « less

Sets appears in: • Ancient Works • Architectural Geology of Italy more » • The Beauty of Building Materials • Integrative Natural History of the Phlegrean Fields • Natural History: Italy • Ortsinn: Landscapes & Localities • Urban Exposures: La città esaminata « less

Camera: MAKER NAME 96660, f/1.8, 1/38 sec, 2.8mm, ISO 50 (more info) (hide info)

Camera:	MAKER NAME 96660
Aperture:	f/1.8
Exposure Time:	0.026 sec (1/38)
Focal Length:	2.8mm
ISO:	50
Exposure Bias:	0 EV
Flash:	Auto, Did not fire
Exposure Program:	Program AE
Metering Mode:	Average
White Balance:	Auto
Color Space:	Uncalibrated
Show full info

Stats: 53 views

go back

Link to this photo view:
Link to this photo large view: