The Ninfeo Ponari is an ancient building dating back to the first century BC, located in the ancient Roman city of Casinum. The building is one of the best preserved examples of 'coenatio aestiva', a leisure annex of a rich 'domus'. It consists of two bodies: a rectangular room covered by a barrel vault and an atrium with no roof and a shallow pool in centre. The structural condition of the building is not critical but its preservation is at risk: it is located on a hill slope where some extended sliding activity is present; it is not protected by an efficient rainfall drainage system. Aim of this paper is to illustrate the strategies and the techniques recently applied to start with a permanent structural health monitoring of the building.