## 1 Introduction  
The importance of historical military architecture is particularly significant in the case of monuments built on earth, and especially abundant when dealing with medieval fortresses in the Iberian Peninsula [1]. The ecological value of the material, the traditional approach of the construction techniques employed, and their territorial scale make this type of heritage of special interest for the development of research and conservation initiatives. International institutions such as ICOFORT (ICOMOS International ScientificCommittee on Fortifications and Military Heritage) highlight the main risks threatening this architectural category. A specific approach to earthen fortifications is in need due to their specific problems and values, which are completely different to other kinds of heritage [2]. In the case of the urban fortified enclosures, and to the normal risks, we must add the pressure of urban development, which throughout history has altered or destroyed a large part of these structures. The emerging sectors of these fortifications nowadays often receive regular maintenance, but also endure physical and mechanical conditions for which they were not designed. The most common transformations of their context derive from topographical operations and changes in the alignment of urban streets, as well as from the demolition and reconstruction of their surrounding buildings. On many occasions, urban changes over the centuries mean that certain sectors of historic earthen walls end up working as retaining elements. This is due to the massiveness and proportions of the defensive ramparts. Nevertheless, this situation was not usually foreseen in the original design of the fortification walls and can lead to a significant physical deterioration of the monument and to situations of structural instability. Often walls in urban areas suffer changes of use, which requires drastic measures to be taken for their conservation as the new use can be incompatible with the original design. For instance, part of the rampart found in Granada [3], which was initially designed to protect the city from flooding of the Genil river ended being up part of a new building. The continuous changes in the initial conditions can damage the wall in the medium/short term. In most cases, as the walls are gravity type structures and are usually very stable, the damage does not compromise the structural stability, although it does lead to weathering and mass-loss processes. In these cases, there are different ways of solving the problem, which usually take into account, among other things, the restitution of the lost material not to compromise stability. In the restoration of several walls in the Generalife of the Alhambra in Granada, an innovative technique of soil projection was applied, in order to restore the lost part of the section because of the water seepage from the backfill [4]. In any case, stability verifications should be performed after any changes have been in use and also whenever the section of the wall is changed. The authors have found that this issue has been inadequately addressed in literature. Despite the large number of studies that address the constructive degradation of military earthen architecture in urban contexts [5; 6; 7; 8], no research has been found on the structural study of cases in which historic ramparts work as retaining elements. This is precisely the main novelty of the topic discussed and developed in this research. Therefore, quick testing tools that can be mathematically validated are in need. However, some interesting experiences approach the assessment of fortified structures with compacted soil from different perspectives, especially in consolidated urban areas. The first approach to this problem is risk management and hazard assessment in these environments. To this end, [PERSON] [5] proposes the use of satellite interferometry as a method to monitor real-time movement of these structures to predict certain behaviors that may pose a threat in the short term.