Structural arcs are very common at the front of mountain belts. The complexity of their internal structures, typically non-cylindrical, is mainly due to the presence of tectonic elements (lateral ramps, strike-slip faults) oblique to the main trend of the belt. In this paper we analyse subsurface data in order to give a quantitative description of a lateral ramp affecting the Northern Apennine front inside the arcuate Emilian folds. A structural contour map of the basal thrust separating the uppermost Apennine tectonic units from the lower ones, and two regional cross-sections, were used to describe and date the interaction of tectonic and sedimentary events that led to the building of the chain. Starting from the Messinian, a deep-seated thrust was responsible for the external buried structures. The tectono-sedimentary activity in the Po Plain subsurface has been going on till the beginning of Quaternary.