In 1470 or early 1471 a minor Florentine painter called Biagio d’Antonio Tucci produced a painting of Tobias with Three Archangels, a variation on the popular Tobias theme which Verrocchio and Leonardo had also tackled.66 Behind the figures is the familiar view of Florence – walls, towers, hills and, in the middle, the great dome of the cathedral. It is conventional enough, but Biagio painted what he actually saw, and what he saw was a tall and rather complicated wooden scaffolding around the marble lantern on top of the dome. The painting thus becomes a unique visual record of the finishing touch being applied to the dome. The main structure of the cupola had been completed nearly fifty years previously by Brunelleschi – ‘challenging the sky itself’, as Vasari memorably phrased it – but it had never been crowned with the orb and cross specified in Brunelleschi’s original design. This project was now entrusted to Verrocchio & Co., and if one could apply some kind of magical magnifying-glass to Utili’s painting one might discern certain figures perched aloft on the scaffolding, and one of those figures might be Verrocchio’s assistant Leonardo da Vinci.
This prestigious contract had been awarded to Verrocchio by the cathedral’s fabbriceria, or works department, in September 1468. The following spring he travelled to Venice and Treviso to purchase high-quality copper for the orb. The finished orb – or, as it is invariably called, the palla or ball – was 8 feet in diameter and weighed more than 2 tons.67 According to Vasari, the casting ‘required much care and ingenuity, to make it possible to enter the ball from below, and make it proof against damage from the wind’. The mould for it is probably the ‘sphere’ mentioned in the post-mortem inventory of Verrocchio’s possessions.
On Monday 27 May 1471 the ball was hoisted to the top of the marble lantern which tops the dome, 350 feet above the ground. The ledgers of the Opera del Duomo record the payment of 2 lire ‘to buy bread and wine for the workmen when they put up the ball’. The work of installing it and securing it to its plinth took three days, then on 30 May the cross was placed on top of it. Among the crowd watching below was the apothecary Luca Landucci: ‘They placed the cross on the said ball, and the canons and many other people went up, and sang the Te Deum there.’ The accounts note that 3 lire was paid ‘to the trumpeters of the Palagio [i.e. the Signoria]… for their trouble when they played on the lantern when the cross was put up’.68
Leonardo certainly had first-hand knowledge of the project, and of the engineering problems involved. A memorandum in one of his notebooks contains a specific recollection: ‘Remember the solders used for soldering the ball on Santa Maria del Fiore.’69 This note is datable to c. 1515, when he was involved in a scheme to manufacture parabolic mirrors, made of a number of facets soldered together. He is looking back more than forty years to that vertiginous Florentine project in which he had assisted as a young man.
It cannot, of course, be proved that Leonardo was perched up on that scaffolding high above the rooftops of Florence, ‘challenging the sky itself’. But where else would we expect to find him?
The project drew Leonardo close to the work of the already legendary figure of Filippo (or Pippo) Brunelleschi, the master architect of the dome, who had done so much to give a new status to the Renaissance architect-engineer. He was a small, ugly, combative man: he was ‘insignificant to look at’, says Vasari, ‘but his genius was so commanding that we can surely say he was sent by heaven’. The famous anecdote of the egg summed up the man’s provocative flair. In the competition to build the cupola, we learn, Brunelleschi refused to divulge his plans, but won the competition with a kind of wager or dare. He said ‘that whoever could make an egg stand on end on a flat piece of marble should build the cupola, since it would show how intelligent each man was’. An egg was duly brought, and the competing experts tried in vain to make it stand on end. Then Filippo stepped up and ‘graciously taking the egg he cracked its bottom on the marble and made it stand upright.’ The others complained that they ‘could have done as much’, but Filippo laughed and said ‘they could also have vaulted the cupola if they had seen his models.’70 This incident is probably apocryphal, but its mix of showmanship and originality (what we would call ‘lateral thinking’) is right, as is the strong motive of professional secrecy. He was plagued by fears, often justified, of piracy and plagiarism – another Brunelleschian feature inherited by Leonardo.
The dome remains one of the wonders of European architecture – it is still, nearly 600 years later, the largest masonry dome in the world. According to modern estimates it contains some 4 million bricks and weighs about 36,000 tons, and it was built without a ‘centring’ (a wooden framework to support the masonry). It is in fact two domes, one nestling inside the other: the larger one measures 180 feet between its opposite edges. Each dome is formed of eight self-supporting arching segments, built simultaneously and reinforced by circular hoops.71 One of Brunelleschi’s innovations was the introduction of safety harnesses: only one mason fell to his death during the building of the dome – a remarkable record by the standards of the day.
The placing of a 2 ton copper orb or ‘ball’ on top of the dome posed engineering problems not dissimilar to those originally confronted by Brunelleschi – primarily how to get it up there. Leonardo’s involvement in the project would have provided him with direct access to the cathedral workshop, and to Brunelleschi’s famed designs for hoists and cranes. Studies recording the overall forms and some of the details of Brunelleschi’s devices are found in a clutch of Leonardo drawings in the Codex Atlanticus; these are generally dated to the late 1470s, but probably reflect this earlier involvement in cathedral engineering. The same machines are found in the notebooks of other Renaissance engineers, but the way Leonardo isolates and analyses particular components strongly suggests he was working directly from the original machines.72 One drawing shows the collo grande (‘big neck’), a machine built by Brunelleschi in 1421, which served as the main hoist for lifting worked stone and other heavy materials to the top of the cathedral. Its particular feature was a gearing mechanism which meant that the hoist could either raise or lower materials without the animals turning the windlass at its base having to change direction. Another drawing shows Brunelleschi’s revolving crane, designed to provide a stable and precise way of placing worked stones during the construction of the dome. Another gives detailed sketches of a crane running on circular rails. All these devices would have been directly relevant to the hoisting and placing of the copper sphere.73
Florence cathedral, showing dome, lantern and orb.
On a folio of the late 1480s, thinking about a naval attack system, Leonardo notes that he must ‘make a cast of one of the 3 screws at the Opera di Santa Liberata’.74 This is another name for Florence’s cathedral, and he is referring to yet another Brunelleschi mechanism – for keeping cables at high tension – to be found in the cathedral workshop. At around this time Leonardo was himself thinking about domes and cupolas, in connection with a project at Milan cathedral. Close reflections of Brunelleschian architecture are found in his studies for this, and a later drawing shows the herring-bone arrangement of bricks in a dome, again echoing the great prototype in Florence.75
Technical study by Leonardo of Brunelleschi’s reversible hoist.
One can today make a vertical pilgrimage to the base of the lantern of the Duomo. A stairway of 463 stone steps leads up from an entrance on the south side of the transept, debouches briefly at the lower rim of the cupola – where one walks past the huge sandalled feet and flapping hems of the Vasari fresco of the Last Judgement – and then twists up behind the wainscots of the cupola to emerge on top of the city, with the rooftops of the old centre spread below, and the streets radiating through them like the spokes of a slightly squashed bicycle wheel. One can see the line of Via Ghibellina where the bottega was, and the tall spire of the Badia marking the site of Ser Piero’s office, and then looking north there is the huge sandstone cube of the Palazzo Medici, still looking as if it has just been rolled into place.
Here Leonardo stood on an early summer’s day in 1471. One senses the grandeur of the occasion for him – in part a euphoria from the bird-like altitude, and in part a sense of the powers of Brunelleschian technology, the precisely calibrated magic which could throw up this gravity-defying structure halfway to heaven. It is an inspirational Renaissance moment.