I once heard of a tradition in Turkey that Leonardo was invited to Istanbul to paint a portrait of “Mehmed the Conqueror” (Fatih Sultan Mehmet) but was unable to accept the commission. No documentation exists to corroborate this story. But there is manifest evidence of Leonardo’s contemporary, the Venetian painter Gentile Bellini, journeying to Constantinople and painting the defining portrait of the Sultan familiar to all Turks. Dating to 1480, it now hangs in the National Gallery, London.
In 1500, after the French invaded Milan and imprisoned Leonardo’s patron, Ludovico Sforza, Leonardo found himself out of a job. Accompanied by his mathematician friend Fra Luca Pacioli and his own feckless assistant Andrea Salai, he left Milan and set out on the road in search of new employment. He traveled east to Mantua and Venice, and worked for a time in Venice as a military engineer. It was in Venice that he apparently came into the circle of merchants trading with the Ottomans. By 1503 he had also abandoned Venice, and for a time served in the employ of the notorious Cesaré Borgia. Then, with the assistance of his friend Niccolo Machiavelli, he had secured a commission that would pit him against his arch-rival, Michelangelo. The two titans of the High Renaissance were to paint a pair of immense murals side-by-side in the Pallazo dela Signoria in Florence. Like so many projects during his career, however, his mural, the “Battle of Anghiari,” would also fall by the wayside. But in 1502-1503 Leonardo applied for a position in the Court of Fatih Sultan Mehmet’s successor, his son Sultan Bayazid II, a leader also known by the moniker “Bayazid the Thunderbolt” (“Yildirim Beyazit”). Subsequent developments, however, would proceed at a pace distinctly different than that of a thunderbolt.
In his letter Leonardo proposes four separate projects to the Sultan:
• “I have a design for a gristmill powered by wind, without the need for running water.” (Nothing new here! Two hundred years earlier the Chinese made windmills, and six hundred years earlier, the Persians. And well before either of them, Heron of Alexandria in the 1st Century AD is thought to have made a working windmill.)
• “I have developed a bilge pump to remove water without the use of ropes and pulleys,” wrote Leonardo.” (Here he has a hydraulic apparatus in mind, and drawings exist for that purpose among his notebooks.)
• “I, your faithful servant, understand that it has been your intention to erect a bridge from Galata (Pera) to Stambul… across the Golden Horn (‘Haliç”), but this has not been done because there were no experts available. I, your subject, have determined how to build the bridge. It will be a masonry bridge as high as a building, and even tall ships will be able to sail under it.” This bridge is the subject of the present story.
• “I plan to build a suspension bridge across the Bosporus to allow people to travel between Europe and Asia. By the power of God, I hope you will believe my words. I will be at your beck and call at all times. — Architect/engineer Leonardo da Vinci” (The letter is dated 3 July, but the year is not specified.)
Leonardo’s sketches for the bridge are found in Manuscript L, a small Codex stored in the Institut de France, Paris, a distance of 2300 km (1400 miles) from Istanbul. A bird’s eye view of the bridge shows the ends flared outward, in the manner of a swallow’s tail. Just below the bird’s eye view drawing appears the graceful silhouette of the bridge, the smooth curve of its runway set atop a parabolic arch, a masterpiece combining form and function! The specs are given in units of braccia, where 1 braccia=0.61 m or 2.1 ft. The bridge is meant to span the 400 braccia (240 m or 800 ft) wide Golden Horn, with its parabolic arch rising to 70 braccia (43 m or 146 ft) above the water. Its runway is smoothly extended to a length of 600 braccia (366 m or 1200 ft) on facing shores; and is tapered in its width at its peak to 40 braccia (24 m or 80 ft). The mathematics for the parabolic support for a bridge would not be worked out as a structural engineering problem until the 19th century, but Leonardo appears to have intuitively realized that this shape provided an especially strong support for the bridge.
In an inventory of its holdings published in 1938 the Topkapi lists the letter as E-6184. The official/scribe identifies the author as “Ricardo ‘the kafir’ of Genoa (the year of the letter is not given.) The word “kafir,” describes an unbeliever, an infidel. It is ironic that the official gets both the name and the city wrong. The letter, in fact, had arrived on a ship sailing from Genoa, possibly causing the confusion in the attribution. It was not until 1952 that the German scholar von Franz Babingen unequivocally established the connection between the letter in the Topkapi Archives and the drawing in the Institut de France.
Leonardo fails to secure an appointment to the court, never gets to see Constantinople, the Bosporus or the Golden Horn, or to offer precise specs for the bridge based on his own measurements.
The Golden Horn, or Haliç to Turks, is an inlet, an estuary on the European side of the Bosporus measuring 10 km or 6 miles in length and 240 m (800 ft) in width at its entrance. It’s direction is East-West. The first bridge to span the Golden Horn was created in 1845 and lasted approximately 18 years. In distinction to the Golden Horn, the Bosporus measures 30 km (18 miles) in length and 3.329 km (2.1 miles) in width at the northern entrance and 2.8 km (1.74 mi) at the southern entrance. The direction is North-South. Thus the fourth project in the letter, a suspension bridge over the Bosporus, would have been entirely impractical in a time before high tensile steel cables could be produced in the 20th century. At its widest point the straits measure 3.4 km (2.1 miles) and even at its narrowest, 700 m (2300 ft). A pair of suspension bridges were built in 1973 and 1988, respectively. A third bridge is presently under construction, and so is a tunnel below the Bosporus near its Southern opening.
Next: Part 3. “Vebjørn Sand and Variations on a theme of Leonardo”
The visionary Norwegian artist Vebjorn Sand resurrected Leonardo’s idea in his design of a bridge over Highway 18 joining Oslo and Bergen. Overcoming local political resistance, Mr. Sand spearheaded the construction of a pedestrian and bicycle bridge. His bridge, scaled down to approximately 25-30% of the size planned for the Golden Horn by Leonardo, was opened in 2001 in Ås. The next installment in this series will explore, “Vebjørn Sand and Variations on a theme of Leonardo”