The bays of Naples and Pozzuoli host volcanic areas that have been active within recent history. In addition, the vicinities areas around the Vesuvius volcano and the Campi Flegrei caldera are extremely densely inhabited. Over the past decade, this situation has prompted several active seismic experiments focused on the Vesuvius volcano. More recently, the Serapis active seismic survey covered the entire Bay of Naples, with particular attention to Pozzuoli Bay. The processed Serapis P wave travel time collection, extended with a previously acquired data set, has allowed the computation of the most comprehensive three-dimensional P wave velocity distribution for the Bay of Naples, which includes a small-scale high-resolution model of the Campi Flegrei caldera. The joint interpretation of the velocity distribution together with both the available gravity measurements and models and the geothermal drilling information has allowed us to locate and map lithological units at depths. We propose a model of the Campi Flegrei caldera in relation to the underlying Mesozoic limestone unit. In this model, no magma chamber exists in the upper 6 km beneath the Bay of Naples. The feeding system of the Campi Flegrei caldera is directly controlled by the tectonic structures affecting the limestone unit beneath the Bay of Naples. Two NE-SW normal faults run beneath the Vesuvius volcano and Campi Flegrei, which are related to the pre-Pleistocene Apenninic tectonics.