This document develops as a study of the effects the earthquakes have on ancient masonry structures. Seeing as these are not prepared for the actions caused by this phenomenon, the injuries this type of building receives are normally quite important. As a result of this, the prevention of these injuries on the buildings is what motivates us to realize this document. The prevention starts first localizing the different lesions in the buildings and classifying them in certain categories depending on their importance and origin. The important thing is that a majority of the lesions caused in an earthquake have a principal lesion that is its cause. So as a main concept we will prevent the principal damage, eliminating this way the originofthesecondaryones.