A great number of Roman millstones have been discovered in the archaeological site of Byrsa at Carthage since the nineteenth century by different international archaeological teams which have excavated the site. Most of these millstones ( catilli/metae ) are hourglass-shaped, and all are made of igneous rocks whose source was identified through petrochemical study. The location of the artefact rock source was determined by comparing thin sections of samples taken from black and red-brownish lava catilli found at the Byrsa Roman site with geological samples taken from Tunisian volcanic rocks located in the northern-western part of the country (Nefza and Mogods regions). The comparison shows that the volcanic petrological and geochemical compositions (basalt and rhyolitic ignimbrite) of the catilli are not from local sources where basaltic and rhyodacite outcrops have been identified in the Guelb Saad Moun (Mogods region) and in the Nefza region respectively. The comparison with existing literature data on similar rocks from Italy has constrained the volcanic origin of the exploited lavas. Thus, the diversity of volcanic rocks (basalt and rhyolitic ignimbrite) suggests several outside origins, such as the Pantelleria Island for the black lava mills and Sardinia (in the area of Mulargia) for the red-brownish lava mills, where these two types of igneous rocks have been widely identified.