The longevity of old mortars

The study of old mortars has revealed a treasure of knowledge concerning the binders and their use in manufacturing mortars as well as the philosophy on which the building technology of the past was based. In this paper the characteristics of mortars taken from some important monuments with remarkable durability are presented and commented on so as to enable their resistance to weathering to be highlighted. Comparing them within the frame of modern durability issues, it could be said that the principles on which the design of long time resistant materials is based are diachronic.