Wealthy patrons and religious orders favoured the arrival of Neapolitan paintings in Tuscany during the Seicento even outside of private collections, particularly in places of worship. The phenomenon reached its peak in the 1680s thanks to the presence of Luca Giordano, only to come to an almost abrupt end. In the 18th century, contemporary Neapolitan painting appears not to have left any particular trace in Tuscan churches, with the exception of a 'San Gennaro' by Francesco De Mura in the central church of San Michele in Borgo in Pisa, executed in 1762 but set up inside the church only in 1775. Although an isolated example, the work enjoyed a certain notoriety locally and was almost always mentioned in city guide books from the late 18th century onwards. Later it was mistakenly believed to have been lost in the bombing that half-destroyed the church on 20 June 1944. Even scholarly studies on De Mura failed to intercept the Pisan canvas, geographically remote compared to the artist's main production. The aim of the present research, therefore, is to draw attention to this interesting work from De Mura's later activity, attempting to reconstruct its models, its history and its commission. A singular circumstance, at once public and private, concerns the person who commissioned the work, the Pisan count Giacinto Catanti, brother-in-law of the Tuscan marquis Bernardo Tanucci, deus ex machina of the politics of the kingdoms of Naples and Sicily from 1734 to 1776, thanks to whom the former was able to pursue a diplomatic career on behalf of the Bourbon monarchy from 1762 to 1775.