The conservation of architectural heritage encompasses various aspects of technical sciences. In large buildings, made and further modified in different stages with different materials and techniques, it is difficult to measure the “health” of its structure in a simple way. The monitoring through displacement gauges represents one of the less costly solutions for estimating the evolution of damage in an existing structure: evidence of damage is represented by an increase of displacements. Anyway, due to the nonlinear behavior of large constructions, it is possible that displacements are measured only when the damage is at an advanced stage. In this sense, urgent measures have to be taken for ensure the stability of the construction. A preliminary study of the monitoring system and a good calibration of the threshold displacement values is required in order to limit the uncertainty about the true damage evolution stage. At the end, a full example illustrating the strategy to adopt in monitoring an historical construction is proposed
