Archaeometric study of ceramic materials from archaeological excavations at the Roman iron-working site of San Giovanni (Portoferraio, Elba Island)

In the framework of the AITHALE project , which promotes systematic research on Elba island through a cooperation among various Institutions (Soprintendenza ai Beni Archeologici della Toscana, Universities of Firenze and Siena, Scuola Normale di Pisa, IGG-CNR, Musei Archeologici elbani), archaeological excavations were carried out in 2012-13 at San Giovanni, in the eastern end of the Portoferraio Bay. The site, known as one of the main ironworking centres during the Roman period (3rd -1st cent. BC.), but possibly even earlier, occurs at the foot of the promontory on which the Roman “Villa delle Grotte” was built in the 1st cent. BC. Abundant waste heaps of metallurgical production occur on the site, mainly including slag, pieces of ore charge and fragments of furnaces. Previous (2009-11) geophysical prospecting on the site revealed subsurface structures, which after recent excavations appeared to be walls and other remains of a Roman farm devoted to wine production, possibly the pars rustica of the neighboring Villa delle Grotte. Samples of different kinds of “ceramics” (bricks, dolia, metallurgical furnaces) were taken both from the farm and a trench dug through the earlier (underlying) metallurgical debris. Archaeometric analysis provided us with interesting information on production technologies and the origin of the raw materials used at San Giovanni in Roman (and pre-Roman?) times. Broken pieces of refractory ceramics, partly slagged and vitrified, commonly occur in the metallurgical heaps. They are constituted by clay tempered with abundant quartz and lithic fragments in order to augment its refractoriness; rare fragments of tuyeres and channels for slag tapping have been found as well. Apparently, iron smelting furnaces at San Giovanni, unlike those found in the Etruscan site of Baratti-Populonia in the mainland, were not (or only partly) armored with refractory stones. Mud clay bricks from the Roman farm, in accordance with recipes reported by Latin authors (Vitruvius, Pliny the Elder ), are made with clay, sand, and organic materials (straw, etc.). The composition of temper used for roof tiles shows significant variations, indicating either imports from different production centres or re-use of old roof tiles. Finally, we analyzed fragments of dolia, the large ceramic containers used for the storage and fermentation of wine. The employment of lithic fragments of basaltic to trachytic composition as dolia’s temper may point to a production area in the medium Tiber Valley, which hosted - in the 1st cent. B.C. - at least one famous figlina (pottery workshop) specialized in the production of opus doliare.