###### Abstract
Nevertheless, the consequences are not always evident and require a detailed study to assess how it can affect the intrinsic characteristics of the rock. Usually, the methods to assess the mechanical effects of fires require destructive techniques that, due to the preservation requirements, cannot be applied in heritage areas. In those cases, the use of non-destructive techniques (NDTs) is necessary [9; 18; 19]. These techniques allow the characterization of materials and the assessment of their deterioration, and they can be applied in situ [9]. Therefore, the NDTs provide wide information in a short period of time without affecting Cultural Heritage [18]. There are multiple techniques used for the study of the physical properties of rocks, such as the Ultrasonic Propagation Velocity or the Leeb rebound hardness test. These techniques allow measuring the effects of high temperatures in the internal structure of the rock. However, their use may be limited if the rock attained very high temperatures and the fracturing degree is large. In these cases, an evaluation of mineralogical changes may be used to assess the extent of damage generated in the rocks because of a fire [20]. One technique widely used in the geological study of rocks is the measure of the magnetic susceptibility [21]. However, to date, this technique has never been applied to the evaluation of the effects of the fires on heritage. The magnetic susceptibility is defined as the capacity of a material or substance to be magnetized when exposed to an external magnetic field. A magnetic susceptibility meter is a tool extensively used in outcrops as it allows quick measurements and therefore allows for surveying large areas quickly. As magnetic susceptibility depends on the composition of the rocks, it permits detecting mineralogical changes that are not macroscopically visible without having to sample [21]. According to their magnetic properties, the materials are classified into three different groups with increasing values of susceptibility [22]: diamagnetic (such as quartz and calcite), paramagnetic (such as muscovite and biotite), and ferromagnetic. Specifically, the diamagnetic have a magnetization opposed to the external magnetic field (so their susceptibility value is negative), the paramagnetic susceptibility is positive since the acquired magnetization is in the same direction to the external field and for both, dia- and paramagnetic material, the generated magnetic field disappears when the external magnetic field does. The ferromagnetic minerals present a magnetization even when the external magnetic field is absent, called remanent magnetization, and their magnetic susceptibility is the highest [22]. Other complementary techniques encompassed in the \"magnetism of rocks\" analyses provide information about the nature and possible coexistence of ferromagnetic minerals. Among them, the \"hysteresis cycle\" refers to the graphic representation of the magnetic variation by the applied magnetic field and it has a characteristic shape depending on the type of mineral. The thermomagnetic curves represent the variation in a magnetic property with temperature in a heating and cooling cycle. The magnetic property can be the saturation magnetization or the magnetic susceptibility. Although these techniques are destructive, they allow to obtain more information and characterize magnetic minerals more precisely and refine onsite susceptibility measurements. The main aim of this work is to test the capability of portable magnetic susceptometers to assess, at least qualitatively, the maximum temperature reached during a fire in an archaeological context. To do so, onsite measurements in an archaeological site affected by a wildfire in recent years were combined with more accurate laboratory measurements to perform a calibration curve of maximum temperatures.