By Marco Vigato
I have just returned from an incredible trip through Tuscany and central Italy, during which I had the opportunity to visit again the fascinating site of Cosa, overlooking the Tyrrenian sea and Mount Argentario. The ancient city of Cosa is surrounded by 1.5 kilometers (1 mile) of polygonal walls built of huge limestone blocks perfectly fitted together to reach a height of nearly 8 meters (26 feet). The earliest written sources on Cosa date to 273 BC, when the Romans established a colony on the site of what was certainly already a very ancient city. Although the construction of the megalithic walls of Cosa is usually attributed to the Romans, their origin may in fact predate the Roman occupation by several hundreds, or even thousands of years. The Romans seemingly appropriated a much earlier site, as is evident from the addition of towers to the original megalithic walls (which, in their original form, lacked towers or any other obviously defensive features).
At Cosa, as at many other megalithic sites in Central Italy, like Alatri, Norba and Segni, the summit of the Acropolis was occupied by a large stepped platform built of huge interlocking polygonal stones, which probably served as an altar and may have been used for astronomical observations. On top of this platform, the Romans built a large temple (or Capitolium) dedicated to the Capitoline Triad. The temple is remarkable in that it shows at least three different styles of masonry belonging to three entirely different epochs of construction. The earliest foundations are built of enormous polygonal stone blocks and are still largely intact. An Etruscan-style temple was then built over these foundations, characterized by a regular masonry of small rectangular tuff stone blocks.
Finally, the later Roman temple, whose walls can still be seen standing to a considerable height, was built of smaller stones cemented together. Elsewhere, like in the area of the Forum, the reuse of earlier megalithic structures by the Romans is also evident. A particularly remarkable example is a vast cistern or reservoir, which may have been once covered by a roof, partially hewn out of the natural bedrock and partially delimited by a huge megalithic wall of large polygonal stones. Cosa lies close and was probably meant to control another mysterious megalithic structure known as the “Tagliata”, an immense rock-hewn channel and water tunnel that many speculate may have been designed with the purpose of connecting Mount Argentario (then an island off the coast of Tuscany) to the mainland by means of a 7 kilometers-long dyke.