Gaetano Cattaneo (1771-1841), founder of the Numismatic Cabinet of Brera, inherited in 1815 from Giuseppe Bossi the historiographical materials that the secretary of the Brera Academy had collected with the aim to create a work dedicated to the history of Lombard art. Cattaneo also devoted himself to the project of a History of the arts and artists of the Lombard school, which never came to light, although its preparation is largely documented by his correspondence with Italian and foreign scholars, such as Cicognara, De Lazara and Passavant. A trace of Cattaneo’s work survives in an unpublished manuscript, kept in the Biblioteca Ambrosiana. In a schematic form, the document reconstructs the history of architecture in Lombardy from the Middle Ages to the sixteenth century, though it was supposed to be continued until the early nineteenth century. The information provided by Cattaneo about the origins of the different “epoche”, in which he divides the developments of Lombard architecture, as to the distinctive structural and stylistic characteristics or as to the masters and their main works offer a very interesting insight into the Milanese historiographical consciousness in the time between French domination and Restoration. The essay considers in particular the judgment on the different phases of the Middle Ages, with particular regard to the profile of Longobard architecture and the origins of the Milan Cathedral. In this case both local debates and the work of Seroux D’Agincourt are fundamental for Cattaneo. Another significant theme is the judgment on the architecture of the sixteenth century in Lombardy, which re-evaluates Leonardo, resizes Bramante and, above all, censors the protagonists of the Borromean age, from Galeazzo Alessi to Francesco Maria Richino. In this respect, the internal debate at the Brera school of architecture and the historiographical positions of Carlo Bianconi and Giuseppe Bossi played an important role, other significant latest sources such as Francesco Antonio Albuzzi and Venanzio De Pagave. The essay reports the complete edition of Cattaneo’s text according to the Ambrosian copy, which was probably made by his collaborator Carlo Zardetti.