An effective assessment of the static and dynamic structural behavior of historical monuments requires the development and validation of suitable adaptive structural models using high quality experimental data acquired with an effective continuous and distributed monitoring. Furthermore, this adaptive strategy allows an effective evaluation of the health status and of the evolution along the time of a historical monument, providing relevant information to plan appropriate actions for its long-term preservation. The Trajan Arch in Benevento was chosen as a case of study to develop and apply this new adaptive strategy in cultural heritage preservation. The paper, after a description of the innovative monitoring system, based on state-of-the art mechanical sensors, presents and discusses the results of two tests, comparing the measurements with the predictions of an adaptive structural FEM model developed for the dynamical simulation of the Trajan Arch.