The sketches on the recto of this newly discovered double-sided sheet vividly illustrate the parallel paths of Leonardo's artistic and scientific genius. The upper portion of the recto represents three sketches of the centrifugal swirling currents of water around obstacles, all seen from above (as if they were plans). Immediately below is a three-quarter view of the currents by a bridge, and to the right, a sketch of a slender nude man unsheathing a sword. Toward the bottom right is the magnificent sketch of the muscular, nude Hercules seen from the front and holding a club horizontally. On the verso, the same figure of Hercules is seen from the rear. On the basis of figural style, drawing technique, and scientific content, the sheet can be dated around 1506–8, shortly, before the artist abandoned the Battle of Anghiari mural for the Great Council Hall of the Palazzo della Signoria (Florence). During those years, Leonardo moved back and forth between Florence and Milan, in the service of both the Florentine Republic and the French rulers occupying the city of Milan. The drawings of Hercules on the sheet are of great historical significance, for they shed light on a mature project by Leonardo that had hitherto remained mysterious. It is now clear that at the time of the work on the Battle of Anghiari, Leonardo was considering a composition of Hercules. Because this sheet represents the figure of Hercules from the front and the rear (see verso), it is clear that Leonardo intended the studies for a sculpture.

As is especially evident from the verso of the sheet, Leonardo appears to have been inspired by a classical sculpture for the portrayal of Hercules. In representing Hercules holding the club horizontally, Leonardo reinvented him as an image of preparedness, not unlike the symbolic allusion to civic vigilance that is evoked in Michelangelo's marble David (Florence, Galleria dell'Accademia), from 1501–4. In view of the close professional interaction between the two artists at this time, it is worth pondering whether Leonardo did not in fact conceive of his Hercules sculpture with a civic function in mind, and in competition with Michelangelo. Leonardo had been among the artists and artisans helping judge the location of Michelangelo's David in 1504, when it was decided that it would stand at the entrance to the Palazzo Vecchio, facing the Piazza della Signoria. Leonardo was Michelangelo's famous rival in the mural projects of the Great Council Hall of the Palazzo Vecchio in 1503–8. It is also well known that Michelangelo himself had considered a Hercules to flank his David in front of the Palazzo della Signoria. At a much later date, in 1526 or so, Baccio Bandinelli would plan and produce such a figural group for the site.

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