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

Dolia are large pottery containers used in Roman times for the storage and fermentation of wine. Together with bricks and other building materials they constituted the so-called “opus doliare” and were probably produced in the same specialized ceramic workshops (figlinae). Opus doliare was typically marked with specific epigraphical stamps, which represent a major tool to unravel their provenance and trade. In this work we present the results of a study - conducted in the framework of the AITHALE project - related to the origin of two dolia defossa recently found at S. Giovanni (Portoferraio, Elba Island) during 2012-2014 archaeological excavations, which brought to light a Roman farm (1st cent. BC-1st cent. AD), devoted to wine production and constituting the pars rustica of the adjacent “Villa delle Grotte”. Based on archaeological evidences, four different provenance hypotheses have been put forward: 1) Elba Island, where the dolia have been found, although there is no clear evidence of the presence of figlinae specialized in opus doliare on the island; 2) the municipal figlinae of the territory of Pisa, where some tiles found at S. Giovanni may have been produced; 3) the middle catchment of the Tiber river (central Latium) where “urban” figlinae occurred; 4) the figlinae of Minturno (southern Latium), a locality known both for wine production and exportation and for the presence of ancient figlinae. Minero-petrographic and chemical compositions of the dolia have been compared with those of raw materials available in the four areas cited above. The study focused on the ceramic framework, particularly on lithic fragment in the dolia and their clinopyroxene (Cpx) composition. Lithic fragments show trachytic - latitic composition, which is compatible only with source regions (3)- urban figlinae along the Tiber valley, Roman Magmatic Province - and (4) - Minturno, in the Ernici-Roccamonfina Magmatic Province. Cpx major element composition (cores in the range Wo 43.7-52.8, En 30-47.5, Fs 6.4-22.5 and rim Wo 45.6-51.8, En 29-47.9, Fs 16.6-22.5) is also compatible with a provenance from these two areas. However, optical observation and mineral-chemistry indicate the coexistence of colourless (high-Mg and Si) and pale green (high-Fe and Al) Cpx. These particular features have been commonly found in rocks belonging to the Roccamonfina trachytic series (Ghiara & Lirer, 1976; Giannetti & Luhr, 1983), thus suggesting that Minturno was the most likely production area of the two dolia unearthed in S. Giovanni.