We present the results of the first archeometric study of some Roman millstones and mortars made of volcanic rocks found at the Libyan archeological sites of Leptis Magna and Cyrene. Two millstones from the first site dating from the III century AD and one from the second, also dating from the II-III centuries AD, were found to made from leucite-phonolite lavas from the quarrying area near Orvieto, in the Vulsini Volcanic District (Roman Volcanic Province). These findings provide further confirmation of the central role played by Orvieto in the Roman production and export of millstones. Mugearite lavas from Etna, transitional basalt from the island of Pantelleria, alkaline basalt, probably from Al Haruj-Al Aswad (Central Libya), and high-K calc-alkaline andesite of uncertain geological origin were the other rocks used for the millstones investigated in this study. This evidence clearly indicates a trade in millstones between Tripolitania, Cyrenaica and Central-South Italy.