In 1952 a remarkable document was discovered in the State Archives at the Topkapi Museum in Istanbul.59 At the head of it, in elegant Turkish script, it is summarized as ‘the copy of a letter that the infidel named Lionardo sent from Genoa’. If it is genuine, it is a contemporary Turkish translation of a letter in which Leonardo offered his engineering services to Sultan Bejazet (or Beyazid) II. At the bottom of the text the copyist notes, ‘This letter was written on 3 July,’ but he neglects to say which year. It was almost certainly1503, in which case it was written in Florence, when Leonardo’s mind was full of big technological projects after the Borgia adventure. (That the letter is described as ‘sent from Genoa’ need only mean that it arrived on a ship from Genoa.)
It begins, somewhat like the famous prospectus addressed to the Moor twenty years earlier, with offers of technological expertise: ‘I your servant… will build a mill which does not require water, but is powered by wind alone’ and ‘God, may He be praised, has granted me a way of extracting water from ships without ropes or cables, but using a self-propelling hydraulic machine.’ But these are only a warm-up before the main offer, which is to design and build a bridge over the Golden Horn:
I, your servant, have heard about your intention to build a bridge from Stamboul to Galata, and that you have not done it because no man can be found capable of it. I, your servant, know how. I would raise it to the height of a building, so that no one can pass over it because it is so high… I will make it so that a ship can pass under it even with its sails hoisted… I would have a drawbridge so that when one wants one can pass on to the Anatolian coast… May God make you believe these words, and consider this servant of yours always at your service.
The notebook Paris MS L, intensively in use during the Borgia adventure of 1502–3, contains what seem to be some working drawings connected with this project, though the design departs in some respects from the description in the letter. The drawing shows a beautifully streamlined structure with ‘bird-tail’ abutments. Leonardo captions it as follows: ‘Bridge from Pera to Constantinople [‘gostantinopoli’, 40 braccia wide, 70 braccia high above the water, 600 braccia long, that is 400 over the sea and 200 on the land, thus making its own abutments.’60 The computation is well-informed: the width of the Golden Horn is about 800 feet so ‘400 braccia over the sea’ is exactly right. The proposed length of the entire bridge (600 braccia = 1,200 feet) would have made it the longest bridge in the world at that time.
Sketch for the bridge at Constantinople (left), and Vebjørn Sand’s realization at Aas (below).
The probable source of this project is Leonardo’s brief sojourn in Rome in February 1503. The previous year ambassadors from Sultan Bejazet had been in Rome conferring with Pope Alexander. It is likely that they mentioned the Sultan’s desire for an Italian engineer to build a bridge over the Golden Horn – at the time there was only a temporary pontoon floating on barrels. Among those interested, according to Vasari, was the young Michelangelo: ‘According to what I have been told, Michelangelo had a desire to go to Constantinople to serve the Turk, who had requested him, by means of certain Franciscan friars, to come and build a bridge from Constantinople to Pera.’ Vasari places this during the period of Michelangelo’s dispute with Pope Julius II in c. 1504. Much the same story is told in Ascanio Condivi’s contemporary Life of Michelangelo (1553).61
Leonardo’s visit to Rome in February 1503, in the suite of Cesare Borgia, thus provides the context: he learns of the Sultan’s interest, he sketches a prototype in his notebook, and he pens his bombastic letter with suitable flourishes. It has been argued that the bridge’s design was based on the Alidosi Bridge at Castel del Rio, on the road from Imola to Florence.62 This was begun in 1499, and was probably still under construction when Leonardo could have seen it during his topographical researches around Imola in the autumn of 1502.
Like Leonardo’s parachute, preserved in a small note of c. 1485 and tested in the air more than five centuries later, the bridge has recently been built according to Leonardo’s specifications – albeit some 1,500 miles further north than its intended location on the Bosporus. On 31 October 2001 a scaled-down version of it (100 yards long) was unveiled at Aas, about 20 miles south of Oslo. Designed and built by Norwegian artist Vebjørn Sand, it was made out of pine, teak and stainless steel, and cost about £1 million. It serves as a pedestrian bridge over a motorway.
Leonardo never rests: he works on through the generations, through all the latter-day Leonardeschi – the artists and sculptors and robot-builders and sky-divers whose imaginations are touched by his brusquely captioned little drawings and the concentrated thinking-power that resides in them. ‘It just had to be built,’ Sand was reported as saying. ‘It can be built in wood or stone, in any scale, because the principles work.’ And so the spores of an idea dreamed up in 1503 eventually flower on Highway E18 south of Oslo.63