Leonardo’s original five double folios exhibited here belong to the vast core of technical and scientific studies in the Codex Arundel dating from the time of the Battle of Anghiari. Leonardo here analyzes the theory and practice of burning mirrors, for which he foresees promising possibilities of exploitation on the industrial and military level. He also engages in defining projects for straightening the course of the Arno where it passes through Florence and for deviating the river by channeling it toward the plain of Prato and Pistoia, thus making it navigable. Such initiatives would have again generated huge economic benefits. Lastly, Leonardo makes innovative reflections on mechanics and on the flight of birds.

If we add to the themes dealt with in these five double folios the evidence of his contemporary intense application to the study of geometry (the transformation of solids and the squaring of plane figures in particular), to cartographic production, to engineering, to geological studies, and to anatomy, we can fully appreciate the dimension of the horizons of Leonardo’s research between 1503 and 1506, in spite of his demanding commitment to the great pictorial undertaking of the Battle of Anghiari.