QUARRY IDENTIFICATION AND CHARACTERIZATION OF 2nd CENTURY A.D. ROMAN GRANITE COLUMNS FROM ECIJA (SPAIN)

Rock column is one of the most representative structural elements used in Roman buildings. Its main section is the shaft, a cylindrical conduit between the base and the chapiter. Their decontextualization sometimes makes it difficult their provenance. This is the case of granite shafts coming from the ancient Colonia Augusta Firma Astigi, nowadays Écija (Seville, Spain). In this paper, 52 pieces of granite shafts preserved both along the streets and in the Municipal History Museum of Écija have been studied, to understand the provenance of the granite used in its construction and the type of building where they were employed. An approximation of the granite composition based on the quantity of the main minerals was carried out by digital image analysis. This non-invasive technique allows us to identify the main characteristics of the granites according to their provenance. Additionally, the column heights were calculated according to Roman treatises of architecture. The combination of these techniques allowed us to determine the quarries of the granite columns. The results showed that 20 shafts may come from the Troad region (Turkey), which granite was one of the most commonly used in the Roman constructions on the provinces; although granite from other quarries, i.e. Gerena (Spain) or Forum (Egypt), might have been used in this city during the 2nd century AD too. The relationship between provenance of the granite and height of the column allows us to specify aspects referred to the magnification of buildings or the sponsors of the monumentalization of public spaces carried out in time of the Roman emperor Hadrian