The Sforza Horse Monument

At a Glance

• SubjectThe Sforza Horse Monument
• Artist and contextLeonardo da Vinci (1452–1519) and his Renaissance world
• Period1480s–1499
• ImageStudy for the Sforza equestrian monument.

Contents

1. A monument before Leonardo
2. From a rearing victory to a colossal walk
3. Measuring horses rather than inventing one
4. From model to hollow bronze
5. Vertical and horizontal casting
6. How much bronze?
7. The bronze becomes artillery
8. Could Leonardo's cast have worked?
9. The 1999 horse is a modern sculpture
10. The monument that survives as a process

A monument before Leonardo

The project belonged first to Sforza dynastic politics. Francesco Sforza had risen from military commander to Duke of Milan in 1450, establishing a ruling house whose legitimacy depended partly on turning conquest into hereditary authority. An equestrian bronze could present the soldier-prince as a permanent founder: armoured, elevated and cast in the material of ancient rulers.

In November 1473, Francesco's son Galeazzo Maria Sforza instructed the official responsible for ducal works to seek an artist capable of making such a monument. The early document already considered its location at the Milan castle or on the ravelin towards the adjoining square. ^{[1] [10]} This was not a private memorial hidden in a chapel. It would stand at the approach to the fortified residence that embodied Sforza power.

Patrick Boucheron has shown that the proposed setting mattered politically. Milan's castle stood at the north-western edge of the city and carried memories of Visconti domination and civic resistance. Francesco had rebuilt it despite earlier promises. An equestrian image aligned with a broad forecourt or route towards the city would place the dynasty's founder between fortress and urban public. ^[10]

Galeazzo Maria was murdered in 1476, and the project stalled. His brother Ludovico later revived it while ruling for the young Gian Galeazzo Sforza and then pursuing the ducal title for himself. Honouring Francesco also strengthened Ludovico's claim to be the active guardian and continuator of the dynasty.

Leonardo arrived in Milan around 1482. In his celebrated draft letter seeking employment, he advertised military engineering, architecture, sculpture and painting. Near its close he offered to undertake the bronze horse for the “immortal glory” of Ludovico's father and the Sforza house. ^[1] The words show that Leonardo knew an existing ambition and used it to present himself as the artist who could finally realise it.

This is why a single commission date can mislead. The dynastic proposal dates to 1473; Leonardo offered his services around 1482–83; sustained work probably began around 1487–88; a major restart came in 1490; the colossal phase was pursued into 1493. A source that says “commissioned in 1482” may be naming the employment pitch, while one that says 1492 may be naming the developed colossal project. The sequence matters more than forcing all phases into one contract.

Leonardo's training made the assignment plausible. Andrea del Verrocchio's Florentine workshop handled sculpture and demanding bronze production as well as painting. Leonardo would have known the early development of Verrocchio's equestrian monument to Bartolomeo Colleoni, whose model left Florence for Venice in 1481. ^[1]

Yet experience around a foundry was not the same as having cast a colossus. No sculpture securely attributable to Leonardo survives. In the summer of 1489, the Florentine ambassador Pietro Alamanni reported that Ludovico wanted Lorenzo de' Medici to recommend one or two masters capable of the work. The implication was blunt: the duke doubted that Leonardo could complete it. ^[1]

The request exposes the practical stakes behind courtly praise. A large clay model could demonstrate form, but bronze required another order of knowledge: alloying, furnace output, mould strength, gas escape, metal flow and the coordinated labour of founders. Failure might waste a fortune in metal and leave a ruptured shell underground.

Lorenzo did not supply a replacement. On 23 April 1490 Leonardo wrote, “I recommenced the horse”. ^[1] The phrase acknowledges interruption and marks a new campaign. It also corresponds to a decisive change in the monument's form.

From a rearing victory to a colossal walk

Two early Windsor drawings, RCIN 912357 and 912358, show a mounted horse rearing over a fallen enemy. In one solution a tree stump helps support the raised body; in another the defeated figure participates in the structural group. ^{[1] [4]} These supports were not incidental narrative decoration. A horse balanced only on its hind legs would place extraordinary bending forces at the ankles during modelling, moulding, casting and permanent display.

The rearing design turned the memorial into an image of immediate conquest. Francesco, or an armed rider representing him, rose above a vanquished body. It belonged to a long visual language in which the horse's movement magnified the commander's mastery. At approximately life size, it was already technically ambitious.

Around 1489–90, Leonardo abandoned that arrangement for a horse moving at a measured walk, with one foreleg raised. At the same time, the project expanded to colossal scale—almost three times life size according to the Museo Galileo reconstruction. ^[4] The revised pose was more conventional, but the enlargement made the casting radically harder.

A walking horse distributes its weight through three grounded legs, offering a broader structural base than a rear. The raised foreleg still brings life to the silhouette. Movement could be conveyed through the turn of the head, the shift of the shoulders and the sequence of the feet rather than a violent vertical thrust. The change was an artistic decision inseparable from foundry reality.

Leonardo studied ancient and modern precedents: the mounted Marcus Aurelius in Rome, Donatello's Gattamelata in Padua, Verrocchio's Colleoni in Venice and the ancient Regisole then standing in Pavia. ^[4] These works showed different solutions to the relation between horse, rider, pace and support. They were points of comparison, not templates from which the lost monument can be copied.

The Pavia encounter can be tied to surviving objects. Around the 1490 restart, Leonardo studied the Regisole on Windsor RCIN 912345 and on the smaller Ambrosiana sheet F 263 inf. 91; related Pavia notes survive on Codex Atlanticus 399r. He praised the antique horse above all for its movement and set imitation of ancient works above imitation of modern ones. ^[17] The studies do not disclose the final Sforza pose, but they show observation of a standing monument entering the redesign at the moment when a controlled walk replaced the earlier rear. Antique authority here supplied a problem of living motion held in durable support, rather than a body to be copied intact.

The new campaign generated close study of living animals. Royal Collection sheet RCIN 912317 contains horses drawn in the Milanese military stables and a tiny sketch of the intended monumental pose. Other sheets identify individual animals by owner, colour or type. A large jennet belonging to Galeazzo da Sanseverino, the captain-general of the Milanese army, supplied one measured example. ^[2]

Leonardo did not search for one “perfect” horse and enlarge it mechanically. Different animals offered a powerful neck, a well-shaped head, a suitable croup or a convincing leg. Measurements allowed him to compare their proportions and coordinate selected features within the model.

This work differed from his contemporary study of the human figure. Leonardo tried to relate human proportion to geometric schemes inherited from architectural and medical theory. The horse had no equivalent privileged place in that cosmology. Royal Collection research argues that this freed him to proceed empirically: measure actual animals, record variation and design from observed bodies rather than impose a supposedly divine canon. ^[2]

Measurement also served enlargement. At twelve braccia, a small error in the angle of a fetlock or depth of a chest would become conspicuous and might change the load carried through the bronze shell. Surface anatomy had to remain credible when seen from below, while the interior geometry had to leave room for a core, metal thickness and supports.

Vasari later wrote of a lost book on horse anatomy. A surviving drawing of a large quadruped's viscera suggests that Leonardo investigated more than external form, although no complete equine treatise survives. It is safer to connect the measured stable sheets directly to the monument and treat the extent of a separate lost book as later testimony.

Not every Leonardo drawing of a horse belongs here. He returned to equine motion for the Battle of Anghiari, the Trivulzio monument and late French projects. A rearing animal, by itself, is not proof of a Sforza study. Secure object records, dates, notes and the relation to casting pages should govern inclusion.

The clay colossus of 1493

By the autumn of 1493, Leonardo had produced the enormous clay horse. It was displayed during celebrations for the proxy marriage of Bianca Maria Sforza, Ludovico's niece, to Maximilian, King of the Romans, on 30 November. Court poets praised the “stupendous horse”, and its scale made the uncast model a public demonstration of both Sforza magnificence and Leonardo's power. ^{[7] [10]}

The display is sometimes described as an unveiling of the finished monument. It was a full-scale working model of the horse, without the completed bronze or a securely documented finished rider. A sculptor could use such a model to judge mass and silhouette, impress a patron, and take mould sections. Clay at that scale required an internal armature and continuous care; it was an intermediate object with the public presence of a monument.

The wedding context sharpened its political meaning. Bianca Maria's Habsburg marriage brought prestige and helped Ludovico's effort to obtain formal imperial recognition of his rule. Francesco's giant horse joined a festival that projected the Sforza family across generations: founder, present ruler and international bride.

No surviving drawing provides a complete orthogonal record of the 1493 horse. The measured studies show components; small sketches suggest poses; casting diagrams reduce the body to outlines or cylinders because their subject is metal flow. Later witnesses admired the model but did not describe every anatomical and ornamental choice. A modern three-dimensional horse necessarily supplies missing decisions.

The rider is still less recoverable. The monument was for Francesco Sforza, and early drawings show an armed horseman. Yet the surviving evidence does not establish one final pose, costume, weapon or method of attaching the colossal rider. Reconstructing the horse is already interpretive; reconstructing the entire equestrian group multiplies the uncertainty.

The clay horse was only the beginning of the casting sequence. A colossal solid bronze would have been impossibly heavy and wasteful. Leonardo needed a hollow shell of controlled thickness. He developed an indirect moulding method recorded especially in the second part of Madrid Codex II and in Windsor casting sheets. ^{[1] [3] [5]}

In broad terms, a sectional mould was taken from the full-size model. Those negative sections could be removed, strengthened and reassembled as an outer counter-mould. Inside sat a heat-resistant core approximating the horse's inner volume. The gap between core and counter-mould defined the bronze skin. Metal spacers and fastenings held the two bodies at the correct distance while molten bronze entered the cavity.

Indirect moulding separated the original clay model from the destructive stages of casting. It also made an enormous form manageable in pieces. Leonardo drew hinges, bolts and concentric metal bands to close the mould. He considered pressure on the lower side and explicitly strengthened it so the weight of molten bronze would not burst through. ^[5]

Uniform thickness was essential. A narrow passage could freeze before adjacent cavities filled. A thick pocket would cool differently, consume extra metal and create stress. If the core shifted, one side of the bronze might become thin while the opposite side became excessively heavy. The accuracy of the mould was therefore structural as well as visual.

Leonardo planned to cast the tail separately. Its narrow, projecting curves complicated the main flow and created leverage at the attachment. A separate cast could be joined after the horse emerged from the pit. His note of 20 December 1493 states that he had concluded the horse should be cast without the tail and lying on its side. ^{[1] [5]}

“In one cast” does not mean that Leonardo imagined melting the entire charge in one vessel. It means that the assembled horse body would be filled in one coordinated operation rather than cast as many bronze plates and welded together. Several furnaces had to deliver compatible alloy at closely controlled temperatures before any stream cooled enough to obstruct another.

Vertical and horizontal casting

Leonardo first explored an inverted vertical cast. The horse would stand upside down in a deep pit, its legs pointing upwards. Runners could deliver bronze along the body's high line while the legs served as chimneys for air and gases. Gravity offered an orderly downward fill through the torso. ^[16]

Madrid Codex II folio 149v diagrams four reverberatory furnaces around a pit and shows the inverted animal with its channels. The system also includes an access opening intended to be formed in the cast. Leonardo was designing the final bronze as something founders would need to enter, clean and inspect. ^[6]

Milan's water table undermined this arrangement. A vertical mould more than seven metres long could not be buried fully without encountering groundwater at about five metres. Moisture meeting molten metal is dangerous; steam expansion can damage the mould and throw metal violently. On 20 December 1493 Leonardo settled on a horizontal orientation, with the horse laid on one side. ^[16]

The horizontal pit was shallower, but the flow problem changed. Furnaces and channels had to fill the long body without allowing separate fronts of metal to cool before uniting. The lower side of the mould bore greater pressure. Gases had to escape from local high points rather than simply travel up four vertical legs. Leonardo's revisions show him choosing between systems, not following one miraculous idea unchanged.

Madrid Codex II records why Leonardo wanted several furnaces. Parallel melting shortened the preparation time, distributed wear and allowed furnaces to perform more reliably after their first firing. The notebook sector contains dated entries from 17 May 1491 to 20 December 1493, showing that foundry planning accompanied the sculptural campaign rather than being improvised after the wedding display. ^[3]

Runners carried bronze from each furnace into selected parts of the mould. Vents released displaced air and combustion gases. Reservoirs could feed metal as the cooling bronze contracted. Leonardo had to calculate not only total volume but the sequence in which streams entered, met and solidified.

He even devised pyrotechnic level indicators. Small charges of gunpowder positioned at known heights would ignite as heat reached them, signalling outside the buried mould that the bronze had risen to a given level and that another furnace should be opened. ^[6] The idea converted an invisible internal event into a timed instruction for workers.

Moving the mould demanded another family of machines. Iron reinforcement and packed earth brought the reconstructed mould assembly to around fifty tonnes before bronze was added. Drawings show winches, pulleys, gears, screws, beams and ties intended to turn, lower or raise large sections without losing alignment. ^{[1] [6]}

Some machinery belongs to an abandoned sequence. A device capable of lifting an assembled mould outside the pit does not prove that Leonardo reached that stage on site; it may record a proposal rejected when its weight became clear. The pages preserve design thinking, including discarded operations.

The foundry was therefore not one invention but a temporary production system. Furnaces, fuel, alloy, mould materials, lifting frames, pits, channels, sensors and trained crews had to perform together within minutes. The 1493 model proved that Leonardo could make the visible horse. The casting notes address the harder question of whether the court could turn it into a durable bronze.

How much bronze?

Numbers attached to the monument vary because they answer different questions. Historical discussions mention more than sixty tonnes, about seventy tonnes, roughly 100,000 Milanese pounds and as much as 200,000 pounds. These figures may refer to a proposed charge, an estimated finished shell, metal with casting waste, or later conversions made with different assumptions. ^{[4] [8]}

The Museo Galileo-led digital project reconstructed a horse, core, mould and foundry from Leonardo's documents. Its published model assigns about 43.62 tonnes to the base, 3.575 tonnes to one solid foreleg, 4.138 tonnes to one solid hind leg and 23.397 tonnes to the remaining horse, for 74.65 tonnes of bronze. ^[8] That is a transparent engineering estimate, not a rediscovered Sforza warehouse inventory.

The accompanying Raccolta Vinciana study assumed an average bronze thickness of five centimetres after considering earlier proposed ranges and the need to carry the horse and an estimated 2.5-tonne rider. ^[9] Change the body geometry, shell thickness, leg construction or alloy density and the total changes. Reporting the assumption is more informative than repeating an “80-ton” fact.

Metal delivered to a Renaissance foundry also exceeded the final statue's theoretical mass. Runners, risers, spills and furnace residues consumed material, while alloy composition could change across remelting. Leonardo's problem was not merely acquiring a number of tonnes; it was producing compatible bronze quickly enough across several furnaces.

In November 1494, amid the military crisis triggered by Charles VIII's descent into Italy, Ludovico sent the bronze reserved for the horse to Ercole I d'Este in Ferrara for cannon. ^{[1] [8] [11]} The act is often narrated as the moment war destroyed art. It also reveals the political nature of bronze.

Large quantities of copper alloy were strategic capital. A ruler could embody authority in a monument during peace and convert the same resource into artillery during danger. The Sforza horse competed directly with the material needs of the state that wanted it to proclaim.

The destination is better documented than the popular claim that these exact guns fought at one named battle. The metal went to a court with expert artillery production during a shifting Italian war. It is safest to say that it was diverted for cannon, not to assign every kilogram to the Battle of Fornovo.

Leonardo may have continued work on moulds or notes, but the casting could not proceed without a renewed supply. Around 1497 he wrote bitterly to Ludovico, “Of the horse I will say nothing, for I know the times”. ^{[1] [11]} The unfinished sentence recognises that the obstacle was no longer only technical.

What happened in 1499—and what survived in 1501

When French forces took Milan in September 1499, soldiers used the clay colossus as a target. The episode was recorded later by Sabba da Castiglione and amplified by Vasari, who wrote that the French broke it completely. ^[1] Projectile damage to unprotected clay is credible, and the fall of the Sforza regime removed the patron and workshop structure that could maintain it.

“Completely destroyed in 1499” is nevertheless too neat. On 19 September 1501, Ercole I d'Este instructed his agent Giovanni Valla to ask the French governor of Milan for Leonardo's horse forma, saying that it was deteriorating each day through neglect. Five days later Valla replied that the governor would not object but needed the French king's permission. ^[12]

The Italian word forma can denote a model, form or mould. The correspondence does not let us inventory exactly what remained. It does prove that court agents believed a substantial, transferable remnant existed in Milan two years after the invasion. Target practice may have scarred and partly broken the clay horse without annihilating it; the surviving item may instead have been a casting form derived from it.

No later document securely tracks the transfer. One scholarly hypothesis is that Ercole eventually obtained the remnant and that it disintegrated at Ferrara; another leaves it decaying in Milan. ^{[7] [12]} The final physical loss is undocumented. The strongest account preserves both events: French soldiers damaged the work in 1499, and a neglected forma was still sought in 1501.

This correction changes the meaning of the story. A single spectacular act of vandalism becomes a slower failure of patronage, material and care. The bronze left first. The regime fell. The vulnerable model was attacked. What remained deteriorated while officials negotiated ownership.

The Museo Galileo and engineering collaborators tested reconstructed vertical and horizontal systems with computational fluid-dynamics software. Their model followed Leonardo's channels, furnaces and mould principles while supplying dimensions, alloy behaviour, temperatures, shell thickness and other data that the surviving pages do not fully specify. ^{[8] [9]}

Under those parameters, the horizontal pour filled the cavity in about 123 seconds; the inverted vertical version took about 165 seconds. Simulated defects concentrated in relatively lightly stressed areas such as the neck and raised foreleg and did not compromise the calculated structural resistance. The researchers concluded that a multi-furnace one-pour system could manage the reconstructed seventy-tonne cast. ^{[8] [9]}

This is a significant result. It refutes the easy assumption that the proposal was merely a fantasy too large to analyse. Leonardo identified real foundry constraints and developed a coherent response. The simulation turns his notes into a system whose flows and stresses can be tested.

It does not prove that a 1490s crew would have completed the operation. Software begins with a clean model and specified values. Historical furnaces varied in heat; alloy batches might differ; workers could mistime a gate; a damp mould might crack; channels might clog; the core could shift. Nor does a successful flow simulation prove that the reconstructed horse reproduces the lost model's exact volume.

The best conclusion lies between dismissal and triumph. Leonardo designed a technically serious casting process with a plausible modern reconstruction. The historical experiment never occurred, so its reliability under the materials, tolerances and labour conditions of Milan remains unverified.

The 1999 horse is a modern sculpture

In 1999 a 24-foot bronze horse designed by Nina Akamu was unveiled near Milan's San Siro racecourse. The project grew from Charles C. Dent's campaign to commemorate Leonardo's unfinished undertaking. It powerfully conveys the scale that the Renaissance monument might have achieved, but it is not Leonardo's recovered horse.

Akamu stated plainly that the surviving drawings do not reveal a final pose or complete appearance. She studied Leonardo's horse sketches, anatomy and other works, then made the artistic choices necessary for a coherent modern sculpture. ^[13] Its missing rider and selected stance belong to that interpretation.

The manufacturing method also differs. The modern model was divided into more than sixty mould sections. Bronze pieces were cast separately, fitted, welded and carried by a stainless-steel internal armature; seven large assemblies were shipped to Milan and joined on site. ^[14] Leonardo planned an indirect mould around a refractory core and a coordinated one-pour bronze shell. The modern work demonstrates large-scale fabrication with twentieth-century methods, not the success of his untested foundry.

Calling Akamu's horse a tribute protects both achievements. It honours the disciplined interpretation and engineering of a new artwork while leaving the historical gaps visible. A polished bronze can otherwise make one modern anatomy and gait look like the inevitable form of a lost clay model.

Around 1508–10, Leonardo designed another equestrian monument for Gian Giacomo Trivulzio, the commander who had led French forces into Milan. This later project was a tomb: a life-size horse and rider above a marble base containing a sarcophagus. Leonardo made variant sketches and a detailed cost estimate, but no physical construction is documented. ^[15]

Some technical ideas carried forward, including indirect moulding, yet the patron, date, scale, function and sculptural alternatives differ. Trivulzio drawings cannot fill gaps in the Sforza horse merely because both projects are equestrian. Late studies made in France require the same separation.

The distinction is especially important in modern reconstructions. Adding a rider from a Trivulzio sketch to a horse inferred from 1493 creates a persuasive hybrid that Leonardo never documented. The result may be valuable as speculative art, but it is not evidence for Francesco's monument.

The monument that survives as a process

The Sforza monument never reached bronze, yet it was more than an unrealised image. Leonardo measured actual horses, constructed a colossal clay model, developed an indirect mould, compared casting orientations, designed a multi-furnace foundry and planned the machinery needed to move masses that no one could handle by hand. The project united anatomy, sculpture, mechanics, materials and organised labour.

Its interruptions are equally revealing. Ludovico's 1489 search for another expert shows that Leonardo's competence was questioned. The 1490 restart replaced a spectacular rear with a more castable walk while increasing the scale. The 1494 diversion of bronze shows artistic magnificence yielding to artillery. The 1501 letters show that loss occurred through damage and neglect rather than one clean ending.

What cannot be recovered should remain explicit. We do not know the final rider, every contour of the horse, the precise alloy charge, whether the complete mould was built, or how a real pour would have behaved. Modern simulation demonstrates possibility under stated assumptions. Akamu's horse demonstrates how a contemporary sculptor can turn fragmentary evidence into a monumental tribute.

Leonardo's most durable achievement here is the chain of reasoning between visible body and hidden production. The horse had to look alive, stand securely, separate into mould sections, preserve a uniform cavity, receive metal before it froze and survive release from tonnes of earth and refractory material. The uncast monument endures because its surviving documents expose that entire problem—not because a later bronze has supplied its missing final form.

Continue exploring Leonardo

• Leonardo and Science
• Leonardo's Anatomical Studies
• Portrait of a Lady: The Historic Leonardo Attribution

Frequently Asked Questions

References

1. Royal Collection Trust, “Studies for casting an equestrian monument,” RCIN 912349. View Source
2. Royal Collection Trust, “Studies of a horse,” RCIN 912317. View Source
3. Biblioteca Nacional de España, El imaginario de Leonardo: Códices Madrid de la BNE, chapter I, part 4. View Source
4. Europeana and Museo Galileo, “Two concepts for the statue,” The Colossus of Leonardo da Vinci. View Source
5. Europeana and Museo Galileo, “An innovative moulding process,” The Colossus of Leonardo da Vinci. View Source
6. Europeana and Museo Galileo, “A multi-furnace foundry,” The Colossus of Leonardo da Vinci. View Source
7. William E. Wallace, “Ercole d'Este and Leonardo da Vinci's Equestrian Statue of Francesco Sforza,” Italian Studies 14, no. 1. View Source
8. Museo Galileo, “Non era leggenda il leggendario cavallo di Leonardo”. View Source
9. Andrea Bernardoni, Stefano Mascetti, Matteo Corrado and Alessandro Incognito, “Simulazioni quantitative sulla fusione del Monumento Sforza,” Raccolta Vinciana 38. View Source
10. Patrick Boucheron, “La statue équestre de Francesco Sforza: Enquête sur un mémorial politique,” Journal des Savants 2 (1997). View Source
11. Museo Galileo, “Del cavallo non dirò niente perché cognosco i tempi,” Codex Atlanticus f. 914r-i. View Source
12. Raccolta Vinciana, documentary register, documents 62–63, 19 and 24 September 1501. View Source
13. Nina Akamu, “Sculptor's Statement,” Da Vinci Science Center. View Source
14. Da Vinci Science Center, “The Sculpting of Leonardo's Horse”. View Source
15. Royal Collection Trust, “Studies for the Trivulzio monument,” RCIN 912355. View Source
16. Europeana and Museo Galileo, “Two different casting methods,” The Colossus of Leonardo da Vinci. View Source
17. Città Metropolitana di Milano, Leonardo nel Ducato di Milano, discussion of the 1490 Regisole studies. View Source

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