When can we claim to know and be able to assess the structures of an ancient building?

Time is our great ally. Old buildings from centuries bear their own weight, and the loads due to their use and sometimes they have resisted the stresses of sudden violent events such as earthquakes. Bearing all of this is in our mind an extraordinary test. The existing buildings overcame it and can help us to lean towards a positive assessment of the overall behaviour of their structures. But time also faces us with a peculiar responsibility. The old buildings in their long history are never equal to themselves, they have been sometimes affected by very incisive changes, which may be evident or less visible. Our own fundamental task is to understand the peculiarities of each structure through specific investigations that may highlight the behaviour both overall and local, and that give scientific basis to the operational protocol that is based on the anamnesis, diagnosis and therapy. An essential methodological step to achieve this goal is the architectural diagnostics, based on a specific and accurate survey, with plans and sections, conjugated with targeted investigations on materials. So two buildings have been examined, the cathedral of Siena and the church of Santa Maria Assunta of Monteluce in Perugia (Italy), highlighting the amazing structural singularity and lack of uniformity even in part of the structures that could appear constructively homogeneous. Structures so heterogeneous, not related to a simple scheme and characterised by possible local vulnerabilities, are an unchanging factor of historic buildings and their own intrinsic aspect. A path of anamnesis and diagnosis is so developed as to reach a coherent understanding of the overall consistency of the artifacts, in which a more founded assessment and evaluation of the behaviour of structures of the ancient buildings can be accomplished.