Pozzuoli's Pillars Revisited

Natural History, May, 1999 by Stephen Jay Gould

All these facts point to a coherent conclusion. The minor columns of the central circle and quadrangle also feature the lower zone of barnacles and oysters. These small columns were not re-erected before the mid-nineteenth century. Lyell's frontispiece, and other prints from earlier in the century, show the three large columns without encrusting barnacles and oysters at the base. Therefore, this later subsidence of land (or rise of sea to a few feet above modern levels) must have culminated sometime after the 1840s--thus adding further evidence for Lyell's claim of substantial and complex activity within the geological eye blink of historical times.

For a few days, I thought I had made at least a minor discovery at Pozzuoli-until I returned home (and to reality) and consulted some later editions of Lyell's Principles, a book that became his growing and changing child (and his lifelong source of income), reaching a twelfth edition by the time of his death. In fact, Lyell documented in two major stages how increasing knowledge about the pillars of Pozzuoli had enriched his uniformitarian view from his initial hypothesis of two quick and discrete changes toward a scenario of more gradual and more frequent alterations of level:

1. In the early 1830s Charles Babbage, Lyell's colleague and one of the most interesting intellectuals of Victorian Britain (more of him later), made an extensive study of the Pozzuoli columns and concluded that both the major fall of land (to the level of the clam borings) and the subsequent rise had occurred in a complex and protracted manner through several substages, not all at once, as Lyell had originally believed. Lyell wrote in his sixth edition of 1840:

   Mr. Babbage, after carefully examining several incrustations as also the
   distinct marks of ancient lines of water-level, visible below the zone of
   lithophagous perforations [holes of boring clams, in plain English], has
   come to the conclusion, and I think, proved, that the subsidence of the
   building was not sudden, or at one period only, but gradual, and by'
   successive movements. As to the re-elevation of the depressed tract, that
   may also have occurred at different periods.

2. When Lyell first visited Pozzuoli in 1828, the high-water level virtually matched the marble pavement. (Most early prints, including Lyell's frontispiece, show minor puddling and flooding of the complex. Later prints, including an 1836 version from Babbage that Lyell adopted as a replacement for his original frontispiece in later editions of the Principles, tend to depict deeper water.) In 1838 Lyell read a precise account of this modern episode of renewed subsidence and then monitored this most recent change in subsequent editions of the Principles. He wrote that Niccolini, "a learned architect [who] visited the ruins frequently for the sake of making drawings," recorded a two-foot sinking of the complex from his first observations in 1807 until 1838, when "fish were caught every day on that part of the pavement where in 1807, there was never a drop of water in calm weather."