Ruins are buildings that, for natural or human causes, have lost considerable parts of their architectural form and materials. The surviving structures, exposed to the weather and in continuing neglect, give us the possibility to study and to know more about the technology from the past. Especially in the artificial stones, the mortars are designed differently in each epoch according to the local manners and material availability. Starting from this consideration, the present research aims to illustrate as the characterisation of mortars and the analysis of their state of conservation has a valuable importance in the knowledge of a building in state of ruin. After a macroscopic in situ inspection, a reasonable sampling has been done as base for the following detailed analysis. Case study of an accurate protocol of research is the Church of San Giovanni Battista, a ruined monument located in the rural landscape of Bortigali (Sardinia, Italy) and dated back XIII-XIV century. In this case, considering the inadequate existence of historical sources, mortars have been a fundamental element to reconstruct the building phases of the fabric, previously uncertain.