The Times of Castles Project: A Combined Study of Rocks and Mortars for Geological Provenance

The PRIN 2020 CASTLES Project focuses on studying mediaeval castles in Italy, particularly their chronology and dating through archaeometric analysis of castles walls mortars. The project is based on a multidisciplinary approach and aims at establishing a new chronology for the construction sites of incastellamento (11th-12th centuries).

A multidisciplinary team integrated their expertise into exploring the subject from multiple perspectives. The team consists of archaeologists and historians (respectively the Universities of Siena and Turin), geologists and conservation scientists (University of Florence), and physicists and archaeologists (University of Campania "Luigi Vanvitelli"). The group selected several sites across three regions of Italy (Piedmont, Liguria and Tuscany). The criteria for selecting the castles were: chronology, state of conservation, historical context, available historical and archaeological data, significant historical relevance. Before starting the sampling of the walls structures mortars, and proceeding to the characterization and dating, it was of fundamental importance to geolocate the castles. This is basilar to understand the geology of the areas where the castles were located and be able to identify the supply sources of the raw materials used by workers to build them. The study was carried out by researching geological maps, aerial photographs, drone images, and scientific publications concerning each castle’s area of ​​the Piedmont, Liguria, and Tuscany regions, as well as sampling rocks of outcropping and constituting the walls. Minero-petrographic and chemical characterization of rock and mortar samples were performed, using X-Ray Diffraction Powder (XRPD), Polarized Light Microscopy (PLM) and Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS). The mineralogical and petrographical analyses of the rocks from each castle area were then compared with the components constituting the mortars (aggregate and binder) from the same castles, to identify correlations. It is essential to establish whether the materials used by the workers were sourced locally or from elsewhere. The results of this first step of the research showed that the raw material used in the realization of Ligurian and Tuscany castles was local. The origin of the rocks used to produce lime in Piedmont's castles is uncertain. In fact, limestone outcrops are very rare in the north of the region. Beyond dating, the analysis of raw materials provides important insights into medieval building organization, showing that most of studied castles relied on local geological resources, while changes in supply areas may reflect settlement expansion and/or a different and more complete organization of the sites of incastellamento.