Advances in Achaemenid brick manufacturing technology: Evidence from the monumental gate at Tol-e Ajori (Fars, Iran)

Abstract This paper deals with the archaeometric characterization of the bricks belonging to Tol-a Ajori Gate, one of the most important excavated sites on the Iranian plateau (Fars, Iran), close to the World Cultural Heritage of Persepolis. The archaeological excavations were carried out between 2011 and 2016 and brought to light a monumental building. The wall of the structure is built with mud and fired bricks sometimes glazed that are very similar to the elements of Babylon's Ishtar Gate. Several investigations were carried out on the bricks in order to investigate the technology process and to compare their composition with local clays, as potential raw materials collected nearby the archaeological site. The brick samples were investigated using different analytical techniques (Optical Microscopy, XRD, XRF, SEM-EDX, FT-IR/ATR, TGA, STA and Micro-Raman) to point out differences in chemical and mineralogical composition. Raw clay samples were submitted to XRD, XRF, SEM-EDX and FT-IR/ATR analyses. A wide homogeneity is present for all the considered bricks: Ca-rich clays with quartz-rich temper were used, this possibly suggesting a common raw material origin. Firing temperatures interval was estimated around 850–900 °C. A multivariate data treatment (PCA and HCA analysis) was applied to the XRF data set acquired for both clays and bricks. PCA suggests that Polvar alluvial clays could be the source raw material for mostly of Tol-e Ajori's bricks and more than one clay deposit was probably used.