The “3 Ponti of Comacchio” represents one of the most important architectural monuments in the Province of Ferrara and surely the most significant historical bridge in Emilia Romagna region. The masonry bridge was built in 1632 by the architect Luca Danese and the customer was the Cardinal Pallotta at that time governor of the town of Comacchio, therefore sometimes is denoted as Pallotta bridge. The shape of the bridge is very particular because it was built at the intersection of 5 canals and presents an internal vault composed by 5 groins of rampant barrel vaults. In 1690 two towers have been added and the bridge assumed the present form. Nowadays it is used as a pedestrian bridge. The interest for the structural behaviour of the masonry bridge is due to the rising up, in the last 2 years, of evident cracks interesting as well the internal vault as the staircases in the west side. The masonry structure was analyzed either by Diana program, using an elastic-plastic damaging model for the masonry, as well as by limit analysis algorithms recently developed by the University of Ferrara. One possible reason of the rising up of the cracks is the settlement of the 3 piers on the west side due to the lowering of the water level in the canals for hydraulic arrangement works. Furthermore, in this study, sinking of pillars foundation will be also taken into account.