Leonardo's most grandiose project, on which he worked for over forty years (from 1473 to 1513 at least), serves to define numerous itineraries through the places of his Tuscany.

The attempt to confer a regular course on the Arno River must be counted among the most ambitious projects ever conceived by man for redesigning the territory and its environment. Leonardo's project went beyond any mere engineering initiative, since it tried to make real a dream of art, in a work that anticipated the neo-avant-garde movements of the second half of the 20th century, especially Land Art, a predominant current in American and British art of the 1960s-70s that operated over great spaces.

Based on his autoptic reconnaissance of the territory and study of the historical-geographic sources, Leonardo formulated the project for channeling the Arno from Florence to the Padule di Fucecchio through Prato, Pistoia and the Val di Nievole. Harmoniously converging in his project were the experiences of the ancients, deduced from observations of Etruscan "cuts", Roman aqueducts and "cicognole" ("swan-like" hydraulic machines, that is, with elbow or horn, used to bring water over hills and valleys) up to the artistic-technological innovations developed in the fervid intellectual environment of Renaissance Tuscany.

Testifying to this Renaissance "dream" are remarkable studies, unique in their beauty and originality. The most famous are those found in the Windsor Royal Library, but other autograph pages as well, whose importance has not yet been fully evaluated, must not be overlooked. They range from cartographic surveys to technical calculations, from structural details to the concept of urban planning and territorial management on a grand scale.

To fully understand the project conceived by Leonardo, we must begin by examining his knowledge of the hydrological and geological past of this territory. According to his reconstruction, based on observation of those lakes and ponds still visible in the Valdarno in his time, there existed in the remote past, along the Arno River, two enormous lakes: one stretched upstream of Florence as far as Arezzo and the Val di Chiana and was put in communication artificially with Lake Trasimeno and the Val Tiberina, or valley of the Tiber; the other occupied the plain of Florence-Prato-Pistoia, while the Montalbano, from Serravalle Pistoiese to the Golfolina di Carmignano and Lastra a Signa, formed a natural barrier separating it from the sea, which covered today's Middle Valdarno.

Leonardo dedicated special attention to the marshlands of the Padule di Bientina, the Stagno di Livorno, and in particular to what was called, on fifteenth-century maps, the "New Lake": the Padule di Fucecchio, into which flowed the waters of the Nievole, the Pescia and ‘his’ Vincio. Into this lake, stretching as far as the "Bagno" (Baths) of Montecatini, the "Pistoia Canal" would have flowed, thus allowing navigation down to the sea.

Leonardo studied a system of navigable canals that would touch on almost all of Tuscany's vital centres: from Arezzo and the Val di Chiana to Pisa and Livorno. His objectives were wide-ranging, complementary and destined to interact: draining the swampy areas, irrigating the fields, preventing floods and hydro-geological upheavals, procuring hydraulic energy and resources for production activity, creating a great thoroughfare of fluvial communication favouring transport and commerce and providing a formidable strategic expedient, with dams that could be used to disperse an enemy army or to beleaguer a city without having to deploy soldiers (for example, by depriving Pisa of its river and thus of its resources).

 

Around the middle of the 16th century Vasari wrote that Leonardo «was the first, while still a young man [and thus during his first Florentine period, which concluded in 1482] to speak of the Arno River, and of channeling it from Pisa to Florence».

Already prior to 1500, in what is, in limitative terms, considered his first Milanese period, Leonardo had left traces in the Codex Atlanticus of the project for the "Pistoia Canal". Specifically, on a folio of studies on automating textile machines (f. 1107 r, ex 398 r-a), datable around 1495 (at the time of the Last Supper), he was concerned with obtaining the necessary financing:

«The wool merchants' guild should make the canal, and take the profit from it, said canal passing through Prato, Pistoia, Serravalle and into the lake, and it will be without basins and more durable and will provide more profit for the places through which it passes.»

It has been suggested that these folios by Leonardo dating from the 1490s should be related to the presence in Lombardy of Luca Fancelli da Settignano, architect and engineer to the Gonzaga dukes, who in 1487 was called upon to judge the projects for the lantern on the Milan Cathedral, on which Leonardo too had worked. It was from Milan – in agreement with the Florentine Ambassador, Pietro Alamanni - that Fancelli wrote on August 12, 1487 to Lorenzo the Magnificent, describing the project for making the Arno navigable from Florence (Mulina d’Ognissanti) to Signa, that is, following the natural course of the river. The information reported by Vasari and the descriptions of Fancelli show that it was not yet a question of creating an alternative course for the river, but of «putting it in a canal», as had been decided in Florence as early as August 28, 1347 and was still being proposed in the Disposizioni per l’incanalamento d’Arno [Provisions for channeling the Arno] from 1458 to 1477.

During the first years of the 16th century Leonardo received prestigious commissions as painter from Isabella d’Este and from the Florentine Signoria, but was also, at this time of warfare, "Most Beloved Family Member, Architect and General Engineer" to Cesare Borgia (called by Freud the "most ruthless and treacherous" prince) and a close friend of Niccolò Machiavelli, who helped him to obtain important assignments.

The work on his project for deviating the Arno away from the city of Pisa, then at war with Florence, began on August 22, 1504 with the utilisation of "1000 diggers", but it was impossible to finish the undertaking: «The river laughed at he who tried to govern her», wrote Muratori.

Along with the Gonfaloniere Soderini, Leonardo too became the target of sharp criticism: «That brain never rests from whimsical caprice!» But notwithstanding, both the course of the canal from Florence to Montecatini, which coincides with the route of today's Firenze-Mare superhighway, and that of the canal upstream of Pisa toward Livorno, which seems to anticipate the recent Scolmatore dell’Arno, show that Leonardo's intuitions were based on reasonable, functional grounds.

Every river is a source of life. «When you put together the science of the motions of water, remember to put under each proposition its benefits, so that this science will not be useless» (Ms. F, f. 2). Thus wrote Leonardo, and in the Codex Atlanticus (f. 785 b, ex 289 r-e) we find exceptionally interesting notes, including the dreamy, prophetic one on the utility and gain that would be procured by the new course of the Arno: «Sawmills and water / Fulling mills / Paper / Pile drivers / Mill / Knife-grinders / For burnishing arms / For grinding /gunpowder and saltpetre / Spinning mill for 100 women / in silkworms / For weaving braiding / Lathes for fine vases such as jasper and porphyry. Straighten the Arno / above and below/ it will yield a treasure / at so much per staio /to whoever wants it. – This Arno floods, because it does not discharge/ its waters as swiftly / as the Val d’Arno above fills it -. And the Golfolina does not let them pass / because the valley is blocked with trees. Rivers always / swell until / the swift currents are engorged / in 3 waves».

On the same folio in the Codex Atlanticus (f. 127 r, ex 46 r-b) is a schematic representation of the project for deviating the Arno, with exemplification of the relevant advantages and cost estimates: «Florence / Prato / Pistoia / Serravalle / Lake / Lucca / Pisa. Make at the Chiane di Arezzo such sluice-gates that, when water is lacking in the Arno in summer, the canal will not remain dry, and make this canal wide at the bottom 20 braccia and 30 at the mouth and 2 braccia 2 always here or 4 because two of these braccia will serve for the mills and fields. This will drain the countryside and will yield Prato, Pistoia and Pisa along with Florence more than two hundred thousand ducats a year and they will lend their hands and purses to its aid, and the Lucchesi will do the same. To make the lake of Sesto navigable, let them make the route from Prato and Pistoia and cut out Serravalle and exit into the lake, because there should be no basins or supports, which are not eternal but on the contrary always call for the work of operation and maintenance. If this river ordinarily occupies the width of an arch, make the bridge with 3 of them, and this because of floods. So that the arches of the bridge will be as high as possible because of the flooding of the river that passes under the bridge –».

Leonardo was concerned with bringing the water over heights – which "at the foot of Serravalle" became steep – through technologically and scientifically correct solutions. Around 1503 he was studying great excavating machines (Codex Atlanticus, ff. 3r and 4r [ex 1v-a e 1v-b]), and the «way to drill through a mountain» (Madrid Ms. I, f. 111 r, c. 1495), already at the time of the "Milanese" projects for deviating the Arno.

He even thought of saving on the cost of labour, as well as on time and fatigue: «This canal should be made from mid-March through mid-June, because the peasants, being free from their ordinary work, can be had for low wages, the days are long and the heat does not tire them».

To present the advantages of the canal more convincingly, he frequently recurred to calculations that now seem perplexing. On folio RLW 12279 he calculates, in fact, «56 miles by Arno from Florence to Vico [equivalent to about 92 km, while the real distance today is about 63 km], and by the Pistoia Canal it is 44 miles, and thus 12 miles shorter by canal than by Arno». He reiterates this concept in another note: «By Arno from Florence to Vico 61 miles and by canal 45, that is, 16 miles less».

In 1504 and in 1505 he climbed up Montalbano and trekked over its heights and around them to define the project for the "Pistoia Canal". On the maps, he corrected the positions of many localities, including Golfolina and Serravalle, arriving at a truer geographical picture (Madrid Ms. II, ff. 22v-23r).

But in the summer of 1506, calls to return to Milan and the commissions of the French heightened the tension with the Florentine Signoria. Again in 1513 Leonardo worked on the Florence and Pistoia Canal, noting (Codex Atlanticus, f. 256 r [ex 93 v-a]): «The Bisenzio and the Ombrone will traverse the canal, bringing abundant water … as regards what is needed for its navigation: and the surplus will go to the ordinary mills […]».

In these and other pages, up to his last years, the great artist continued to cultivate projects for the land of his birth, studying how to transform the hydro-geographic system of his Tuscany rationally and functionally: his definitive move to Amboise, at the service of King Francis I, relegated his great land-art dream to the realm of utopia.