Leonardo da Vinci designed a bridge for the Sultan of Istanbul. It was never built, but recent studies have shown that the bridge was an amazing piece of engineering design, so a Norwegian company has built a smaller version from the same plans in Norway and it is a sight to behold!

The Golden Horn

Istanbul, the biggest city in Turkey¹, is divided into three separate regions by the sea. Running from south west to north east is the Bosporus, a kilometre-wide channel of the sea which is traditionally the divide between the continents of Europe and Asia. Up until the last century, the city was entirely on the western (European) side of this channel of water.

More interesting is the deep water inlet known as the Golden Horn. This runs in a westerly direction from the west side of the Bosporus. It divides the old city of Istanbul into two. To the south of the inlet is the original city founded by the Greeks and later expanded by the Romans. Known as both Byzantium and Constantinople, it was the possibly the greatest city in the world for nearly a thousand years. To the north of the Golden Horn is the suburb known now as Beyoglu but for most of its existence as Galata. This started out as a small village but gradually grew to be a sizable suburb of the city.

There was a narrow bridge across the inlet in the 12th century, somewhat to the west of the city, but it was destroyed during the Crusader siege of 1204 and was never rebuilt. By the time the Ottomans captured Istanbul in 1453 and made it their capital, the district of Galata was quite big, but was cut off from the rest of Istanbul by the Golden Horn. The inlet itself is only 300 metres wide, but is very deep, making it difficult to bridge.

The Design

In 1502, the Sultan Bayezid II decided he needed a bridge. He commissioned none other than Leonardo da Vinci himself to design the bridge. Leonardo's design was strange in the extreme: a stone bridge in a single graceful arch, thin at the centre and widening both horizontally and vertically at the ends to join onto the land in a series of curves; the design is organic-looking and resembles the roots of a tree. The whole style of the bridge is a triumph of minimalism, totally unlike the baroque masterpieces popular in Europe at the time.

Some details of Leonardo's design:

• Width at centre: 24m
• Height above sea at centre: 40m
• Span: 240m
• Total bridge length: 360m

We don't know the Sultan's reaction to Leonardo's plans, but the bridge was never built. The inlet remained unbridged until the 19th Century when an ugly and cumbersome floating bridge was built. This was later replaced by the present Galata Bridge.

The Bridge of Aas

The designs for Leonardo's bridge were forgotten about. They were included in an exhibition on the work of Leonardo, but nobody really looked at them until 1996, when Norwegian artist and architect Vebjørn Sand saw the plans and was bowled over by them. He analysed them using modern civil engineering knowledge and discovered that the bridge didn't just look good, it was also a miracle of clever design. The extremely narrow centre of the bridge reduces the load on the sides to such an extent that the weight is not too great, and a single 240m span of stone can cross the entire inlet; nobody has ever built a stone bridge of this size to this day, but it appears that Leonardo's Bridge would have been viable.

But whether it would have remained standing for long is not clear - Istanbul is an earthquake zone, and Leonardo may not have taken this into account in his design.

Sand was so impressed with the bridge that he was determined to build a copy of it. He approached the Norwegian National Roads Authority. They were interested and eventually found a suitable site, in the village of Ås (sometimes written as Aas), where a footbridge over a main road was needed. The road is the E18, the main route from Oslo to Stockholm, so the bridge is seen by many travellers every day. Sand worked with the road engineers and Leonardo's plans, scaling them down to one third size to produce the world's first Leonardo-designed bridge. In keeping with Norway's reputation as a forested country, a combination of wood and stainless steel was used rather than stone. The bridge was opened at the end of 2001. You can see it today if you go to Oleghus in Norway.