'Leonardo da Vinci: Experience, Experiment, Design' is at the V & A, London SW7 (020 7942 2000), Sept 14-Jan 7, 2007
For 500 years, Leonardo da Vinci's most important fresco was believed lost. Martin Gayford reports on exciting rumours of its discovery
Deep in the bowels of the British Museum is a tiny drawing by Leonardo da Vinci. The Battle of Anghiari was to be the supreme depiction of the fury of war, and a summary of Leonardo's thoughts on the violence of human nature. It depicts a miniature but terrible world - a place of desperate struggle in which armed cavalry flail and hack at one another, and horses sink teeth into each other's necks.
From a distance, the twisting, thrashing groups resemble some violent natural phenomenon: wreckage in a whirlpool, say, or the vortex of a typhoon. Peering through a lens at this 500-year-old fragment of paper - which will be included in a forthcoming exhibition of Leonardo's drawings at the V & A next month - I am looking into the artist's mind.
This is one of the few remaining clues to the appearance of what should have been his greatest painting. The Battle of Anghiari, for which this is a sketch, was meant to be his largest and most prominent work. Commissioned in 1503, when Leonardo was 51, it would have been colossal - some 60ft across - and placed at the heart of the Florentine state: the painting was to occupy one wall of the Council Hall in what is now known as the Palazzo Vecchio.
It was to be the supreme depiction of the fury of war, and a summary of Leonardo's thoughts on force, motion and the violence of human nature. And - possibly, just possibly - a substantial fragment of this masterpiece might still exist, several centimetres behind the plaster of a 16th-century wall.
The Battle of Anghiari is the real Holy Grail of Leonardo studies: a wonderful lost object for which the search continues today. Its rediscovery would be an art-historical sensation. War was the stuff of everyday life in early 16th-century Italy, and Leonardo had plenty of opportunity to observe it: he described armed conflict as "the most beastly madness". His previous patron, the Duke of Milan, was a captive of the French - then the regional superpower. When Milanese territory was invaded, Leonardo's equestrian monument to the Duke's father - his greatest project as a sculptor - was used by French troops for target practice, and destroyed.
In 1502, the year before embarking on The Battle of Anghiari, Leonardo had been employed by Cesare Borgia, the most feared warlord of the day, who was attempting to carve out a state in central Italy, the traditional domain of the Papacy. Florence itself - briefly at that time a republic - was attempting to placate Borgia and the French while also waging a war of attrition with the neighbouring state of Pisa. The daily news, recorded by Florentine diarists such as Luca Landucci, was of massacres, ambushes and routs.
Niccol˜ Machiavelli and Leonardo himself were involved in a catastrophically failed scheme to divert the river Arno, and hence deprive the Pisans of water and communications. Meanwhile, the Battle of Anghiari - against the Milanese in 1440 - was one of Florence's few recent victories.
Tantalisingly, since it has disappeared, this painting is the best-documented of Leonardo's works. It is possible to follow in detail his elaborate preparations for this huge work in the Florentine archives. There were payments for the paper and glue required for the cartoon - or full-scale design - and for modifications to the room in which he was working. Wood and paper covers were made for the windows, to create the diffused light which Leonardo liked.
A little later, there were more expenses for the ingenious height-adjustable mobile platform he devised from which to work. Among his papers is a lengthy and gripping account of how Leonardo thought a battle should be depicted. He described the conflict, scientifically, as a sort of atmospheric disturbance: "the smoke of the artillery mingled with the dust tossed up by the movement of horses and combatants". Leonardo talked about the effects of battle on men: "Make the conquered and beaten pale, with brows raised and knit, and the skin above their brows furrowed with pain; the sides of the nose with wrinkles going in an arch from the nostrils and ending where the eye begins; the nostrils drawn high up -which is the cause of these lines."
These ferocious faces of conflict are depicted in his preparatory drawings for the picture, which include not only warriors but also horses, scowling with their lips contracted in fury. According to Prof Martin Kemp, the curator of the V & A exhibition, the painting should have been the "climactic demonstration of his mastery of bodily motion in men and animals". Had all gone to plan, it would also have been one half of the most stupendous two-man show ever held. In 1504, the Florentine government commissioned Michelangelo to paint an equally enormous painting as a companion to Leonardo's.
Michelangelo conceived this work - The Battle of Cascina - as a demonstration of the nude male figure in action. Eventually, well behind schedule in February 1505, Leonardo seems to have been ready to begin the painting. But something went wrong. Later that year, on June 6, he noted that he'd begun work at 9.30 am. "At the moment of putting down the paint-brush, the weather changed for the worse." The bell in the law courts was rung by the wind, the cartoon came loose, rain poured down until nightfall, "and it was dark as night".
In all probability, Leonardo was recording not the moment he began the painting, but an evil omen. The Florentines were very superstitious. Leonardo jotted down a visit to a soothsayer around this time; Landucci the diarist described the ominously unseasonable weather that June.
Certainly, something went badly awry with The Battle of Anghiari. Leonardo was apparently experimenting with a new technique - not true fresco, which bonds with wet plaster, but an oil medium. Using oil paint for a mural was a dubious proposition, but it would have allowed him to work as he liked - slowly, building up subtle glazes.
Later accounts suggest Leonardo was sold linseed oil of such bad quality that there was trouble getting the paint to dry and fires had to be lit beneath it. The picture began to peel. Leonardo completed only his central group, the intertwined melee struggling for the Milanese standard. Eventually, to the fury of the Florentines, he drifted back to Milan to work for the French.
Michelangelo only got as far as completing his cartoon before he was summoned to Rome to work for a new Pope, Julius II. But his design had a vast influence on artists - as did that of Leonardo, which was copied. From those copies, Rubens later made an imaginative version of the central group.
For nearly half a century, the fragment of Leonardo's picture remained on view. Then it was replaced by a fresco by Giorgio Vasari and his workshop. Did Vasari, who revered Leonardo, paint over this vestige of a masterpiece, rather than destroy it?
That is an alluring thought, and a researcher named Maurizio Seracini believes he has located the hidden fresco.
But there is as yet no consensus, about whether or exactly where it might survive - nor how it could be recovered without destroying Vasari's painting. In its absence we have Leonardo's marvellous l ittle drawings, covered with his swirling thoughts.