Geological sources and use of rotary millstones from the Roman iron-making site of Les Martys (Montagne Noire, France)

Roman rotary millstones are commonly reported in ancient mines and iron-making centres around the Mediterranean basin. The millstones from the iron-making site of Les Martys have been found in slag heaps dated at the first century B.C. They are mainly of two types: Pompeian-style mills made of tephritic leucite-phonolite imported from Orvieto (Vulsini, central Italy), and cylindrical handmills made of basalt imported from Agde (southern France). The Pompeian-style mills were presumably used for the crushing of slag residues in order to re-use them as a flux in the reduction of iron.