Provenancing and archaeology of roman millstones from the Mediterranean area

Abstract

Abstract Roman rotary grain mills in the Mediterranean area are mainly of two styles: hourglass-shaped “Pompeian-style” mills and flatter, cylindrical millstones. Many of these millstones are made of igneous rocks imported to the sites where the mills are found, and they may therefore be important indicators of resource procurement and trade if the source of the rock of manufacture can be traced. Three types of igneous rock were used to make millstones: (1) reddish rhyolitic ignimbrite; (2) leucite-phyric lavas and (3) generally fresh grey vesicular lavas of basic-intermediate composition. Potential source rocks and millstones of all three types of rock were characterized using petrographic examination in thin-section, and chemical analysis for major and 15 trace elements determined by low-dilution fusion wavelength-dispersive X-ray fluorescence analysis. One hundred and forty-six millstones and lavas from archaeological contexts were studied, and 113 of these were successfully assigned to geological sources. Sixteen areas of igneous rocks were used by the Romans for millstone production. These include the basic and intermediate composition grey vesicular lavas of Olot (northeast Spain), Agde (southern France), Volvic and possibly the Le Puy area (central and southeast France, respectively), Vulture (Italy), Etna and Monti Iblei in Sicily, Pantelleria, Sardinia, Ustica, the Aeolian Islands, Nisyros (Aegean), Libya and the Middle Atlas and Rif areas of Morocco. The red rhyolite was quarried at the village of Mulargia in Sardinia, and the leucite-phyric rocks originated on the Italian mainland (including the quarry of Orvieto in Umbria). There is a wide variation in size and style of millstones from individual production centres, and some were exported in unfinished form. Grey vesicular millstones were traded up to at least 820 km from their sources and fall into four mainly separate distributions in the Mediterranean. The Mulargia rhyolite and the leucitites were moved mainly from north to south, were traded further than the grey vesicular rocks and were probably the most desirable types. They are found 1350 and 1500 km distant from their sources, respectively. The millstones were moved mainly by sea, perhaps on grain-collecting ships on outward voyages from Italy to the south and west of the Mediterranean.