Leonardo and the Military Engineering

Leonardo’s interest in undertaking charges of military engineering for the Sforza court dates back as far as 1482-83, when he wrote a letter of presentation to Ludovico il Moro. Although his preparation up until that time related primarily to the tradition of workshop artisanship, Leonardo enumerates his capabilities with emphasis on his preparation in relation to military engineering, listing his activities as painter only at the end. Leonardo’s intention was to impress the duke.

During these Milanese years, Leonardo attempted to update his knowledge regarding the art of fortification, which up until that time was limited to what he could get from the mechanical tradition of Tuscany. He came into possession of certain classical and modern texts on the military arts that were in circulation in the Sforza court. Leonardo knew of classical authors through second-hand sources and he paralleled study of these with his examination of the fundamental contemporary text De re militari (On military matters), by Roberto Valturio. Valturio’s drawings of war apparatus, reflect the state of military engineering during the second half of the fifteenth century, in which the mêlée weapons of medieval tradition coexisted with the new firearms, and all were depicted in a fantastical, nearly theatrical, key.

These drawings are characterized not only by their unbridled fantasy, but also by their detachment from any practical implication. Leonardo was fascinated by the extraordinary and dramatic aspects of war-faring engines. Leonardo combined elements from tradition with automations and complex mechanical elements. In his drawings of war machines, engineering interweaves with artistic representation in a manner conferring tones of excitement and drama upon many drawings.

In 1502, Leonardo had his first contacts with the leader Cesare Borgia, son of pope Alexander VI. He was at the head of a state in Romagna created for him by his father. Thus Leonardo’s charge was that of military consultant with the objective of visiting all the fortifications in Romagna for works of repairs and reconstructions.

In 1506 Leonardo was back in Milan, in service to the governor Charles d’Amboise, who praised him for his works of military architecture. During these years, Leonardo drew the Castle of Milan many more times.

The model represents the corner of a stronghold with two square fortifications at the corner: the first is included within the perimeter of the main stronghold wall, while the second protrudes out from the corner with the majority of its volume. The moat is fashioned not by means of excavation but by a retaining wall and large quantities of earth. A particularly interesting feature is the innovative position for the defense of the flanker, which is realized by arranging for a line of firearms on the protruding part of the fortification, so that the defenders could strike any assailants who might reach the top of the moat. The objective of this structure is to be able to organize through successive phases a series of grazing shots to strike assailants at the points where it is most difficult to advance: the bank, the moat, the curtain wall, and the upper patrol walk.

The model represents a ravelin, or a defensive outpost, on triangular plan. Leonardo drew this, with the page turned upside down, in plan and prospect views, giving details about the crown on a separate folio. Its walls are steeply sloping and are divided into two sectors by a ribbing. The much shorter upper sector shows corbels between small arches and loopholes, for positioning of artillery, alternating with embattlements. The corners of the ravelin are blunted, and on the terrace roof there is a covered patrol walk and three small service buildings. Rather than a ravelin, this could be a bulwark of bastions that Leonardo may have seen, possibly referring to the stronghold at Ostia or at Civita Castellana, in Lazio, both of which were on plans of Giuliano da Sangallo.

The model represents a section of fortification and moat, over which two war-faring machines are being used for assault against the walls: a carriage with mobile bridge covered by a roof and an adjustable ladder. These allowed soldiers to position themselves behind enemy walls and to pass over the moats to climb the walls. The bridge could be moved on its rollers and wheels, and it had a covered structure for protecting the soldiers as they crossed. The inclination of the covered bridge could be adjusted using the cables attached to a transmission shaft.

With this carriage, Leonardo rediscovered with admiration, studied, and innovated with the models from the war-faring tradition of the Middle Ages. Of the form of a tortoise, the carriage is reinforced with metal tiles and is shown in an open view to the side to display the interior. It is surmounted by a tower allowing sighting from the inside and armed with cannons. Movement for the carriage was provided from the inside by eight men who actuated a system of gears connected to the four wheels. The direction of fire could be decided by the men positioned at the upper part of the carriage, from where they could view the battlefield through narrow openings.

This ballista, an actual exercise on one of the traditional assault machines from classical and medieval times, was conceived for launching stones with a parabolic trajectory and for a long distance, to open a breach in the enemy walls. It is constituted of a wooden spring that is drawn by a bolt positioned at the base of the trestle structure: the energy for the launch is provided by the extreme torsion of the cords. This instrument of war was conceived for obtaining a great power within modest dimensions, by contrast with the trebuchet, an assault weapon working on the counterweight principle, which often reached over 10 m in height.

This crossbow, a veritable “technological dream”, was to be used, in Leonardo’s intentions, for casting great balls of stone, creating panic and fright among the enemy. The proportions were colossal and Leonardo represented their impact by drawing a soldier operating the weapon, intent on utilizing the trigger system: the arms had a total open span of 42 braccia, about 24 m, mounted on a stock 23 m long and 1.2 m thick. The machine moved on six wheels.

Leonardo describes this diving suit in detail: “Jacket and trousers, and a small skin for urinating, a skirt of tasses, and a skin for holding the air, with half-circles of iron to keep it apart from your chest. If you have a whole skin, with balls for valves, when you deflate it you will go to the bottom with it, drawn by the sacks of coarse sand. When you inflate it, you will return upward, onto the water. A mask with the eyes covered with glass. But have the weight be what you can lift in your swimming. Take a knife that cuts well, so a net will not end up catching you. Take with you 2 or 3 small skins, deflated, which you can inflate like balls if you need” . The leather diving suit, thus, was composed of jacket, trousers, and mask with glass viewing pieces. The inflating of the jacket was sustained by a structure of iron circles, and a skin was provided for containing a reserve of air.

“Circumfulgore is a naval machine. It was the invention of the people of Majolica, and it is made of a circle of bombards, of whatever number you please – as long as it is not an uneven number, since, in order for the blow to be effective, and for the craft not to recoil, it is necessary for one bombard to be at the back of and to block another. And to do this, it is necessary to give fire at the same time to two contrary bombards, so that if one causes recoil toward one direction, the other will contradict it”. The model represents a study of a multiple bombard conceived for positioning on the bridge of a ship. Leonardo called it circumtronito or circumfolgore (roughly surround with thunder or surround with lightning). It is constituted of a section of the hull of a watercraft, on which an artillery turret is installed, composed of a turning platform on which 12 firearm barrels are arranged. The bombards, probably breech-loading, are arranged radially so as to allow them to shoot simultaneously in opposite directions, thus balancing the recoils after shots so that the ship would not be subject to dangerous yawing or rolling.

This winch described and observed by Leonardo was used for raising pieces of artillery, such as bombards, or columns. The winch is of the classical trestle form. At the upper part, a balance-type arm rocks on a pivot: one extremity is connected with an endless screw, while the other bears a bombard tied with cords. The raising and lowering is effected by means of an endless screw and a helicoid wheel acting as screw bolt. The movement causes the central axis on which the cannon is hanging to oscillate slowly, thus raising it.

“New method for a bellows that works very well”. On a folio in the Codex Arundel, compiled in 1508, Leonardo dwells on a breathing system for use in working underwater. Twenty years after his sketches for an underwater diving suit, on a folio of the Codex Atlanticus rich with many military indications for underwater attacks against enemy ships, Leonardo approached this theme again from a new perspective, indicating the utility of the system for the purpose of caulking, meaning the leak-proofing of the ship’s planking by filling in the cracks with oakum.

With this breathing system, a man could work under water without needing to dry-dock the ship. The span of 20 years between these and the earlier drawings of the diver is obvious.

The model represents a swing bridge with parabolic profile constructed over a watercourse. To the left is the end portion of a road constructed on an embankment. The bridge is constituted of an arched span with parabolic profile. The free end, which is thin and light, rests when the bridge is closed upon a support of trunks on the other bank of the river, where the road begins again. The pivot is connected to two winches positioned at the two sides of the embankment and is also provided with a counterweight container for balancing and facilitating the maneuvers when the bridge remains suspended in air, before coming to rest on the other shore. Movement of the bridge is effected by means of cords and winches and with the aid of metal wheels or rollers.