The maps drawn by Leonardo da Vinci pertaining to the diversion of the Arno River covered the territory of Tuscany as far south as the present-day coastal town of San Vincenzo in the province of Livorno. The site along the coast that Leonardo concentrated particular attention on and described in most detail was the promontory of Piombino. On map RL 12277 (Royal Collection, Windsor Castle) Leonardo drew an outline of the peninsula from the Gulf of Baratti, along the Stagno (marsh) of Piombino to the Valle del Cornia. In addition, notes on the territory and various projects for the fortification of the town of Piombino can be found in Ms. L, the Codex Madrid II and the Codex Atlanticus.
Heeding the counsel of Machiavelli, for a brief period Florence recognized Cesare Borgia as the “Signore di Piombino” after his troops occupied the town, taking advantage of the temporary absence of its ruler, Iacopo IV Appiani. It is probable that certain brief annotations (such as those in Ms. L) date to Leonardo’s first visit (in 1502) to the area comprising this strategic port (which existed in antiquity and was called Falesia by the Romans) and the coast between Populonia and Follonica. He studied how the marshlands might be drained and drew up various innovative military engineering projects.
It is certain that in 1504 Leonardo worked for Jacopo IV Appiani, with whom Florence was seeking to negotiate an alliance or at least a promise of neutrality. Although his initial assignment was limited to the objectives laid out by Machiavelli, Leonardo subsequently went further, working out projects that would later form the basis of a series of annotations on architecture that constituted a trait d’union between the Trattato di architettura, ingeneria e arte militare of Francesco di Giorgio Martini and the work of leading engineers in Italy at the turn of the century.
Significantly, some of Leonardo’s notes on the navigation of sailing vessels show that while in Piombino he worked closely with Antonio da Sangallo the Elder. On folio 122r in the Codex Madrid II the words “front line, that is, bowline” and “sternline” were in fact written by Sangallo. Carlo Pedretti retraced the history of this collaboration through the architectural drawings in Ms. L and the Codex Atlanticus (such as folio 115v, which contains surveys for new bastions for the defence of the citadel).
Leonardo had been summoned to Piombino to advise Cesare Borgia and then Jacopo IV Appiani on how to strengthen the town’s defenses. It is interesting to note that in addition to the plans themselves, observations on their strategic objectives and how much they would cost appear in the Codex Madrid II, for example on folios 37v and 38r-v: “We will make a tunnel, or covered way underneath the wall, for relief by the citadel to the ravelin of the door. The entrance to the ravelin will be through a drawbridge, in order to prevent the taking over of the ravelin by breaking through the tunnel from the land side, in case the people had an understanding with the enemy”. Leonardo noted the dimensions and calculated “the total cost for the aforesaid works”, which comprised the moat surrounding the city, the walls of the moat, the rampart and the tower: “the aforementioned tower has a diameter of 25 braccia and a circumference of 78 e 41/7 braccia. Its height is 20 braccia, and it is entirely solid and of uniform thickness until its base…”. The total came to 2099 ducats, to which had to be added another “3000 lire” for the strategic lowering of the height of a nearby hill and for the “the mountain along the seashore”, “which is, in short, 428 and 4/7 ducats, at 7 lire the ducat. Added to the aforementioned 2099 1/16, it sums up to 2528 ducats”.
Quite different in tone are the artist’s notes on the subject of painting and other matters from the period which he spent in Piombino. Here, interspersed among his numerical calculations, are reflections on a variety of topics such as the sensory faculties of animals: “Darkness is privation of light. Shade is diminuition of light […] Among all animals, the cat has the keenest senses of seeing and hearing. And its sense of smell ia almost as good as the aforementioned. Where it lacks visual power, the cat makes it up with its hearing. It always keeps its ear in readiness, like a funnel, to receive the impressions of the noises made in the air, and sends them through long conduits to the common sense”. Knowing how Leonardo worked, it is not surprising to find such digressions on pages filled with engineering calculations and lists of expenses.
The same goes for notes of a scientific nature that are at the same time poetic, such as this passage on folio 125r: “1504 in Piombino, All Saints' Day. On painting. As the sun declining, I saw the green shadows of the ropes, mast, and yard cast upon a white wall. And this was happening because that part of the wall not illuminated by sunshine became tinted by the color of the sea reflected onto the wall.
In Ms. L are notes on La Rocchetta and on “how to dry the marsh of Piombino”, as well as sketches of the hills around Populonia and Piombino.
Codex Madrid II contains further reflections on the architectural theories of Francesco di Giorgio (folio 89r): “If a square tower is provided with pyramids at the corners, with varied shelters, like stairs, ports, double bridges, devious entrances, ravelins and ditches, it will have, by itself, great resistance. In this harbor, 250 feet from its entrance, a wall 80 feet wide and 300 feet long, and escarped with a parapet shall be placed. This harbor suffers not from the sea because wall a b serves as a fortress, as a dike against the waves, as a lighthouse, and is protected from every wind. This harbor has 2 sluice gates, at the beginnings of the walls near the land, which, when opened, allow the rough sea to clean and wash the harbor of any refuse.”
The passage continues on folio 88v, where a construction borrowed from Francesco di Giorgio is described (“Porto di Piombino”), and technical suggestions on how to build foundations under water are provided: “When making foundations in the sea, where there is no firm rock, make 2 circuits of stakes […].” On folio 9r we find references to the tower and moat, with new bastions and subterranean passages connecting to the “ravelin of the gate”. On folios 24v and 25r – amongst drawings of bastions, studies relating to the leveling of the top of a hill and the construction of a firing range, and the ground plan and the section of a new quadrangular fortress – one reads: “The last day of November, All Saints' Day 1504, I made in Piombino for the Lord this demonstration”. In addition he described how for the “fortress of Piombino the 20th of November 1504» «covered way» […] «the moat which I am straightening” his first project consisted of a “covered roadway” running between the already existing citadel and the new tower (which he had designed) and of a “straightened channel” (another tunnel) between the new tower and the principal “gate” of the city, as well as a trench of ca. 380 metres between the citadel (“the fortress on Mount Sancta Maria”) and the Rocchetta. On folio 35r as well there are calculations for the fortifications of Piombino: “Moat, including the walls and enclosure of the fortress, from the mountain to Santa Maria, amounts to 5942 ducats. Moat and the walls of the moats, and the defenses of the terrain, with the tower and its barbicans, 25 braccia thick and 20 braccia high, entirely solid, excepting the defenses, amounts to 2393 ducats.”
Furthermore, while in Piombino Leonardo studied the movement of the waves, the winds, and sailing ships; navigation; the trajectory of artillery projectiles; and the strategic usefulness of lowering the height of the hills around the fortified town. From Piombino he could also observe the island of Elba.
In the Codex Atlanticus are drawings of fortifications that are exceptional not only from an aesthetic and an architectural point of view, but also because they reflect Leonardo’s understanding of military strategy. They can be dated to the early years of the 16th century, when Leonardo received various commissions from Cesare Borgia and Piombino. Even today traces of his work can be seen in the Citadel – for example, the defensive wall on the north side of the town, the buttresses constructed to compensate for the subsidence of the ground, and the wall at the western extremity of the defensive line towards the inland. The ravelin of Porta a Terra is especially noteworthy.
The exactitude of Leonardo’s calculations and surveys (in which he made use of both a compass and an odometer), and of his sketches and notes for the projects that he was working on in the autumn of 1504, deserve to be underlined.