PETROGRAPHY AND STAMPS OF ISTRIAN ROMAN AMPHORAE REVEAL SOURCE MATERIAL AND ANCIENT WORK-PRACTICES; NORTHERN ADRIATIC REGION, CROATIA

The availability of good quality raw material, stone and clay, the principal inorganic materials used in construction and manufacturing in the ancient Roman world controlled the site and success of workshops. Ceramics, in particular amphorae, were the most widespread form of trade-packaging and their distribution can be traced as far as Scotland to the west and the Coromandel coast of India to the east. Geological techniques aid determination of their provenance, ancient technologies and their categorization. This work focuses on the northern Adriatic coast (Istrian region, Croatia) where the Laecanius senatorial family was influential politically and owned one of the largest pottery-workshops (late first century BC to 80 AD). Their amphorae attained a wide distribution, recognized by their characteristic morphology (Dressel 6B) and stamps (Bezeczky 1998). The Laecanius workshop produced around 1 million amphorae during its 80-100 years existence but, during that time, another 30-40 workshops existed in the region. Such a high output indicates that suitable source material was available locally. Thin section, heavy mineral and XRD analyses identify the source of raw material used. Two heavy mineral suites are recognized: a volcanic and a moderately stable one with Alpine affinities. Bauxite is rejected as a clay source, because no bauxite-specific minerals or anatase, common in Istrian bauxites, were found in the ceramics. Terra Rossa, widespread in the region, commonly mixed with loess of River Po (Alpine) provenance and with volcanic grains from Italian eruptions, have similar suites to those found in the ceramics (Durn et al. 1999) suggesting the most likely source. Many fragments contain contemporary marine microfauna, indicating that mud from the seafloor was dredged to use as a temper. Heavy minerals assist in the categorization and grouping of related amphorae, which also show a temporal change in composition, reflecting the use of material from differing sources with time.