Leonardo Sketches the Design for a Double-Decker Bridge

Leonardo’s idea for a double-deck bridge is surprisingly modern.

It recalls the function of bridges in some modern metropolis where the two-way flow of traffic is arranged on different levels.

Leonardo doesn’t mention what this project was actually for, but it is clear that it is a way of organising the two-way circulation system in such a way that doesn’t create traffic jams or obstructions.

Leonardo's study of the motion of water led him to design machinery that utilised its force. Much of his work on hydraulics was for Ludovico il Moro. Leonardo wrote to Ludovico describing his skills and what he could build:
“ ...very light and strong bridges that can easily be carried, with which to pursue, and sometimes flee from, the enemy; and others safe and indestructible by fire or assault, easy and convenient to transport and place into position. ”

Among his projects in Florence was one to divert the course of the Arno, in order to flood Pisa. Fortunately, this was too costly to be carried out. He also surveyed Venice and came up with a plan to create a movable dyke for the city's protection against invaders.

In 1502, Leonardo produced a drawing of a single span 240 m (720 ft) bridge as part of a civil engineering project for Ottoman Sultan Beyazid II of Istanbul. The bridge was intended to span an inlet at the mouth of the Bosphorus known as the Golden Horn. Beyazid did not pursue the project, because he believed that such a construction was impossible. Leonardo's vision was resurrected in 2001 when a smaller bridge based on his design was constructed in Norway. On 17 May 2006, the Turkish government decided to construct Leonardo's bridge to span the Golden Horn.