The structure of walls and buildings found in archaeological sites can vary widely due to the numerous decay processes affecting the stone and mortar components. Decay processes owed to natural factors, as well as those stemming from the history of the region (e.g., wars and reconstructions), and those om any previous restoration attempts, all affect the shape and strength of wall buildings. With regard to the method of mortar preparation (e.g., water and aggregation medium content) and the various components used therin, both affect the durability of walls and buildings constructed with mortar. In the medieval village of Montarrenti, near Siena, mortar samples were collected from walls and buildings in various state of decay. Samples were collected from both walls and buildings of different ages. The aim of this study is to emphasize how the technology of mortar preparation coupled with the bonding and aggregation components of mortar, affect the durability of mortar structures.