To the east of the castle of Vinci, at the point where the watercourses that are tributaries to the Streda collect, Leonardo had projected the construction of an artificial lake. The project, recognized in three drawings identified and studied by Renzo Cianchi, the first librarian of the Biblioteca Leonardiana, is a surprising demonstration of the perfect knowledge Leonardo had of the places of his childhood. All the sketches represent the same hydrogeological system, that is, the series of streams descending from the slopes of Montalbano, to join together toward the southeast, at the place called Serravalle. The project included the territories of the communities of Faltognano and of San Lorenzo in Arniano, and part of the community of Santa Croce. In the maps of the Capitani di parte Guelfa relating to these communities, we find details of the waterways and places included in that project which was the most exquisitely "Vincian" that Leonardo executed (Windsor maps RL 12675 and RL 12676, Codex Atlanticus, f. 952r).

Leonardo's project is reported in three different maps representing the same system of waterways. The almost perfect coincidence of their drafting with that of the streams that still descend from the eastern slope of Montalbano allows us to precisely identify the streams as drawn by Leonardo. The watercourse to the right is certainly the Rio di San Lorenzo with its small tributaries, flowing into the valley below the hill where the church of San Lorenzo in Arniano was situated. The ecclesiastical building, today in a state of ruin, is reported on two of the project maps, depicted as a double rectangular area (RL 12676). The central watercourse is certainly the Rio del Lecceto mentioned by the statutes of Vinci: Leonardo, in fact, reports the toponym lecceta on the slope under which that watercourse flows. The last watercourse involved in Leonardo’s project is the one that was called the Rio di Gello in the 19th century, which flows through the small valley situated between the slope of the place still today called Gello and Poggio Marradino, the hill facing the castle of Vinci, under which the stream Streda flows. The three watercourses, the Rio di Gello, the Rio del Lecceto, and the Rio di San Lorenzo, flowed together and then went to augment the brook Streda, downstream, just below the castle, in a place known today as Serravalle. The barrages on the streams at their lowest point of confluence would necessarily cause the most depressed part of the area to fill, which in the maps is indicated with crosshatching, to form the artificial basin. The basin would have been fed by the waters of the three streams by means of water intakes allowing regulation of the input until completely filled. The watercourses were then diverted outside the perimeter of the artificial lake, resulting in an isolated and completely governable system. The purpose of this system of captation and control of the waters of the Faltognano streams, as Renzo Cianchi hypothesized, must have been related to a mechanical use of hydraulic power, perhaps to feed water wheels in an area that is, and was, very rich with mills. During Leonardo’s time, the waters of the Rio di San Lorenzo powered at least one mill, the mill di Arniano, mentioned in the statutes of Vinci. Right in this little valley, there is still a mill in ruins today. It is not impossible that Leonardo's drawings referred to a larger public utility project conceived for the community of Vinci. Moreover, the municipal statutes show a constant and particular care toward some watercourses, including the Rio di San Lorenzo and the Rio della Lecceta. The public nature of these watercourses would suggest, therefore, a project commissioned, or otherwise agreed upon, with the municipal authorities of Vinci.
Leonardo knew these places very well. Browsing through the properties that his father declared in the 1498 land registry, we read of numerous lands situated in the places crossed through by the streams depicted by Leonardo for this project. The town indicated as a Gello, in the community of Santa Croce, was mentioned several times among the da Vinci family properties. In Faltognano and in the community of San Lorenzo in Arniano, Leonardo’s family owned lands and estates in the localities of la  Noce and Capannile, which are located near the sources of Rio della Lecceta. The place Leonardo indicated as lecceta on one of the maps for the project corresponds to the locality Novelleto delle monache del paradiso (Novelleto of the nuns of paradise), where Ser Piero claimed to have a plot of land rented from the nuns themselves. In these areas, therefore, they possessed lands for cultivation, olive groves, wooded areas, and areas containing vines (vineyards), houses, and farmhouses, two of which, in San Lorenzo, were uncovered, without roof or beams. The landscape is that of the western slopes of Montalbano, those that look towards the castle of Vinci and that can still be admired today. It is suggestive, today, to retrace the paths that cross through the hills and valleys that were being observed by Leonardo at the time when he conceived of the project of the artificial lake in that valley which perhaps, then, he could have called the valley of the Altoviti. This was the name used by the Capitani di Parte Guelfa, in one of their 16th-century maps, to indicate the point where the artificial lake of Leonardo’s project was projected.
Texts by
Silvia Leporatti / English translation by John Venerella