Pozzuoli's Pillars Revisited

Natural History, May, 1999 by Stephen Jay Gould

I had brought only the first edition (1830-33) of Lyell's Principles with me to Naples. In this text, Lyell attributes (tentatively, to be sure) all changes in level to just two discrete and rapid events. He correlates the initial subsidence (to a level where marine clams could bore into the marble pillars) with "earthquakes which proceeded the [1198] eruption of the Solfatara" a volcanic field on the outskirts of Pozzuoli. "The pumice and other matter ejected from that volcano might have fallen in heavy showers into the sea, and would thus immediately have covered up the lower part of the columns." Lyell then ascribes the subsequent rise of the pillars to a general swelling and uplift of land that culminated in the formation of Monte Nuovo (a volcanic mound near Pozzuoli) in 1538.

But at the site, I observed with some surprise that the evidence for changing levels of land seemed more extensive and complex. I noticed the high zone of clam borings on the three columns, but evidence--not mentioned by Lyell--for another discrete episode of marine incursion struck me as far more obvious and prominent, and I wondered why I had never read or heard anything about this event. Not only on the three major columns but in every part of the complex--the minor columns at the corners of the quadrangular market area, the series of still smaller columns surrounding a circular area in the middle of the market, and even the brick walls and sides of structures surrounding the quadrangle--I noted a zone extending two to three feet up from the marble floor and terminated by a sharp line of demarcation. Within this zone, barnacles and oyster shells remain cemented to the bricks and columns--so the distinct line on top must represent a previous high-water mark. Thus, the still higher zone of clam borings does not represent the only episode of marine incursion. This lower, but more prominent, zone of shells must signify a later depression of land. But when?

Lyell's original frontispiece (redrafted from an Italian publication of 1820), which includes the bases of the large columns, depicts no evidence of this zone. Did he just fail to note the barnacles and oysters, or did this period of marine flooding occur after 18307 I scoured some antiquarian bookstores in Naples and found several early-nineteenth-century prints of the columns (from travel literature about landscapes and antiquities, not from scientific publications). None showed the lower zone of barnacles and oysters. But I did learn something interesting from these prints. None depicted the minor columns now standing both in the circular area at the center and around the edge of the quadrangle--although these locations appear in some prints as flat areas strewn with bric-a-brac. But a later print of 1848 shows columns in the central circular area. I must therefore assume that the excavators of Pozzuoli re-erected the smaller columns of the quadrangle and central circle sometime near the middle of the nineteenth century--while we know that Lyell's three major columns had stood upright since their first discovery during excavations in 1749. (A fourth major column still lies in several pieces on the marble floor of the complex.)