TRAJAN’S FORUM (HEMICYCLE) AND THE VIA BIBERATICA (TRAJAN’S MARKETS) : AN HHPXRF STUDY OF THE PROVENANCE OF LAVA PAVING IN ANCIENT ROME ( ITALY)

摘要

This paper reports on geochemical data collected using a He-enabled handheld portable XRF (HHpXRF) from lava paving stones in Trajan’s Forum (Hemicycle) and the Via Biberatica (Rome). Issues relating to HHpXRF field use and calibration are also addressed in detail. By means of this instrument, 355 analyses of the paving stones were collected and the data were processed using the standard techniques of igneous petrology and petrography. Provenancing was based on comparisons between the HHpXRF data and geological data from the abundant literature on Roman volcanic rocks. These comparisons placed the provenance of the paving stones in the Colli Albani, south-east of Rome. Further analysis using Zr/Y versus Nb/Y discriminant diagrams suggests that the paving stones were quarried from two sources, both of which are represented in Trajan’s Forum and the Via Biberatica. The diagrams suggest that the sources lie within the Faete and Vallerano lava complexes. The latter were probably transported to the construction site by barge on the River Tiber and the former were easily accessible by carts along the Via Appia. The study establishes the potential of HHpXRF equipment for non-destructive analysis of paving stones both in Rome and at other sites in central Italy, and challenges a number of assumptions about the supply of building materials to Rome based on intuition alone.