Archaeometric analysis of Roman bricks from Noricum

A brick is a brick, one may think, a simple rectangular piece of clay, less than ever attractive, which is of no interest unless it is included in an impressive building. Yet bricks have been part of the building technology for millennia and have become the hallmark of Roman architecture, to such an extent that brick walls not only have ears, they also have a story to tell. There are many ways in which bricks can give us information on the past. Sometimes, we find intentional stamps and inscriptions that can be used to date the structure and to give an identity to the builder; on other occasions, accidental paws and fingerprints left on fresh clay frame a moment of everyday life that seemed insignificant at the time but takes on a certain importance now. These are the events that bricks can tell us directly, but what if we are not so lucky in finding these marks or if we want to look further and discover other messages? In this case, a little help from material science and analytical techniques is required. By studying the chemical and mineralogical composition of bricks we can figure out the ingredients used in their manufacture, their provenance, the recipes and the firing strategies. Mechanical and physical analyses will give us an indication of their resistance, degradation rate, and suitability for construction. Unfortunately, the study of a few adobes is not enough to get the complete picture because, although they look almost identical, bricks are not all the same. Differences or similarit ies can be found depending on the raw materials, the manufacturers, the intended use or on how the technique was transferred and learned. If we consider the Roman province of Noricum, the main actors of the diffusion of the adobe building were the military. Whether they stayed for short periods or settled permanently, they chose bricks to realize many structures and produced them on site. Production required a certain organization to find the clay pits, transport and mix the ingredients, build the kilns, etc. All these operations involved local workers and expertise and were adapted to the needs, resources and traditions of the place, having an impact not only on the architecture but also on the economy and landscape. Aim of this project is tracing the evolution of the brick technology in Noricum. To do that, I will follow a precise path, starting first with the analysis and comparison of samples from the same site and then from different sites, taking into account the chronology of the foundations, archaeological data and also historical and epigraphic sources. The final step is the comparison with the materials from Aquileia, the city from which many soldiers were recruited and where it can be said that everything began. The combination of archaeological, architectonical, historical and chemical- physical knowledge is fundamental to embark on this journey, and at the end of it, we may discover that, after all, these are not just bricks in the wall.

Have you ever wondered about the possibility of analyzing archaeological objects without touching or sampling them? This has become possible thanks to new analytical techniques and portable instruments. However, the accuracy of the results obtained through these methods is not always as reliable as the more destructive classical ones. In order to ensure their reliability, a comparison between the two analytical approaches needs to be made. The testing ground was ceramic building materials, particularly Roman bricks from the archaeological sites of Celje (Slovenia), Lauriacum (Enns) and Albing-St Pantaleon, where the Legio II Italica built their military camps between the 2nd and 3rd centuries A.D. By using minimally invasive tools, I was able to identify markers that helped reconstructing the brick recipes and determine the temperature at which they were fired. How was it possible? The firing process causes clay to decompose and create new mineral phases that are dependent on the temperature reached. Contactless reflectance infrared spectroscopy allows for verification of the presence of these phases by monitoring the shape of signals that correspond to the vibrational movements of specific atomic bonds. For more accurate compositional data, we need X-ray diffraction. This time we have to scratch the object's surface a bit, but it is worth it because, with a few milligrams of sample, we can tell what raw materials were used to make it and where they were extracted. Additional information is given by studying the object's porosity with X-ray microtomography. This method enables the visualization of the object in 3D and is crucial in order to identify weak spots that could lead to fractures. Moreover, the size, shape, and orientation of the pores provide valuable technological insights. These are just a few examples of minimally invasive analyses but with these and various others measurements, I could trace the path of the production of bricks in Noricum. In short, when the production started (Celje), bricks seemed to be manufactured in harsh with irregular mixtures, then (Lauriacum) the recipes became slightly different: the mixtures were still rich in inclusions but smoother. However, the bricks were mainly fired at lower temperatures or unevenly. Finally, in the Late Antique (St.Pantaleon), the same recipes are maintained, but firing temperatures become higher and more uniform, indicating an improvement in firing technology. These results encourage us to continue in the direction of non-destructive analysis, even though we are not dealing with a statue but with simple bricks.