PROVENANCING OF LIGHTWEIGHT VOLCANIC STONES USED IN ANCIENT ROMAN CONCRETE VAULTING: EVIDENCE FROM TURKEY AND TUNISIA

The mastery of the use of lightweight rocks in concrete as a means of controlling the thrusts of large‐scale vaults was among the most important contributions of the Roman builders to the development of vaulted architecture. The string of volcanoes along the Tyrrhenian coast of Italy produced a variety of lightweight rocks, which allowed the builders in Rome to develop highly sophisticated ways of manipulating form and mass to create stable structures. The use of lighter rocks in vaults and heavier in foundations occurs from the mid‐first century bc in Rome, but the systematic use of imported lightweight rocks only began in the early second century ad under Trajan ( Lancaster 2005 , 59–64). Soon thereafter, the technique of using lightweight stones to build large vaults spread throughout the empire, usually to areas that had a local source of lightweight volcanic material. However, there was also a seaborne trade in lightweight rocks to areas that did not have local sources of such material. The intention of our analysis is to determine as precisely as possible the provenance of the lightweight stones used in vaulting of two areas of the Mediterranean, modern Turkey (ancient Cilicia) and Tunisia (ancient Africa Proconsularis), and thus to provide a better understanding of the nature of this trade.