###### Abstract  
Wildfires are one of the main threats of natural areas and often fires can affect protected or heritage areas and properties, in which the preservation requirements demand the use of non-destructive techniques (NDTs). The magnetic susceptibility is an NDT that provides information on the mineralogical composition of the materials but has never been applied to the evaluation of fires. Here, we combine laboratory with field analysis to test the applicability of the magnetic susceptibility for the assessment of the impacts of wildfires. The laboratory results showed an increase in the magnetic susceptibility with the temperature, more evident in the samples heated to 600 \({}^{\circ}\)C and above. The in situ measures revealed a spatial variation in the magnetic susceptibility, which was related to the behaviour of the fire in the area. The samples were later analysed with other magnetic destructive techniques that were used to confirm the mineralogical processes that occurred in the materials. The increase in the susceptibility values were due to the formation of iron oxides. The destructive analysis also showed the presence of minerals such as hematite and magnetite in the samples. Overall, the study allowed a first approach to test the magnetic susceptibility as a simple and fast way to measure the impacts of wildfires. f 20  
oxidize and emit to the atmosphere ashes, carbon dioxide, water, and other compounds as well as producing light and heat. The high frequency of the fires implies that they often affect big areas with singular elements of Cultural Heritage and, particularly, Archaeological Heritage. Cultural Heritage includes all the items (material or immaterial) that represent a physical or spiritual part of the presence and practices of the societies along its development and, therefore, deserve to be conserved for future generations. A large amount of Cultural Heritage is built on stone, and it is susceptible to be altered and destroyed by fires [5; 6; 7; 8]. This deterioration can be defined as the degradation through time of the properties of a material (physical, mechanical, chemical, etc. ), as well as its characteristics (mineralogy, texture, etc. ), that can derive in its structural failure [9]. Fire damage of heritage will become more frequent due to climate change and increasingly common conflicts in locations with archaeological sites [6; 10; 11]. The high temperatures generated during fires generate a series of changes in the mineralogy and petrophysical properties of the rocks that can derive instability problems. Consequently, it is important to assess the effects that these problems can generate in the structure of stone buildings and structures [12]. The importance of wildfires as a decay agent of Cultural Heritage is because of the catastrophic damage generated in a short period of time with long-lasting effects [13]. Previous research suggested that the impact on the rock depends on the velocity at which the maximum temperature is reached and the time that the rock is exposed to high temperatures [14]. When a rock is heated during a fire, there is a steep temperature gradient from the surface to the interior. This phenomenon can be highly destructive instantaneously, as the high temperatures generate rapidly a thermal stress that can cause a thermal shock due to the formation of microfractures [15]. Thus, the most visible effects of degradation can be found on the first centimetres of the material. One of the most noticeable effects of high temperatures is the structural damage found at different scales [8]. There are mineralogic changes and different fracture patterns at small scale that control the macroscopical physical and chemical degradation. The alteration of the mineralogy and the porosity, which conditions the amount of water that goes into the rock after the fire, determines how the rock decays in the long term [16; 17; 12].