The oldest recorded bridge over the Golden Horn in Istanbul was built during the reign of Justinian the Great in the 6th century close to the area near the Theodosian Land Walls at the western end of the city. In 1453, during the Fall of Constantinople, the Turks assembled a mobile bridge by putting their ships next to each other and used it for transporting their troops from one side of the Golden Horn to the other.

Golden Horn Bridge designed by Leonardo da Vinci in 1502

In the years 1502–1503 plans to construct the first bridge in the current location were discussed. Sultan Bayezid II solicited a design and Leonardo da Vinci, utilizing three well-known geometrical principles, the pressed-bow, parabolic curve and keystone arch, created an unprecedented single span 240 m long and 24 m wide bridge for the Golden Horn, which would have become the longest bridge in the world of that period if constructed. However, the ambitious design did not meet with the Sultan's approval. Another Italian artist, Michelangelo was also invited to design a bridge for Istanbul. Michelangelo rejected the proposal, and the idea of building a bridge across the Golden Horn was shelved until the 19th century.

A smaller scale version of Leonardo da Vinci's Golden Horn Bridge was brought to life in 2001 near Oslo, Norway by the contemporary artist Vebjørn Sand, the first civil engineering project based on a Leonardo da Vinci sketch to be constructed. The Leonardo Bridge Project hopes to build the design as a practical footbridge around the world, including the Golden Horn in Istanbul, using local materials and collaborating with local artisans as a global public art project. The Wall Street Journal referred to the Project as a "...logo for the nations." (WSJ, Nov. 5-6, 2005)

The second bridge

This bridge was replaced by a second wooden bridge in 1863, built by Ethem Pertev Paşa on the orders of Sultan Abdülaziz (1861-1876) during the infrastructure improvement works prior to the visit of Napoleon III to Istanbul.

The third bridge
Galata Bridge, late 19th century

In 1870 a contract was signed with a French company, Forges et Chantiers de la Mediteranée for construction of a third bridge, but the outbreak of war between France and Germany delayed the project, which was given instead to a British firm G. Wells in 1872. This bridge, completed in 1875, was 480 m long and 14 m wide and rested on 24 pontoons. It was built at a cost of 105,000 gold liras. This was used until 1912, when it was pulled upstream to replace the now genuinely old Cisr-i Atik Bridge.

The fourth bridge

The fourth Galata Bridge was built in 1912 by the German firm MAN AG for 350,000 gold liras. This floating bridge was 466 m long and 25 m wide. It is the bridge still familiar to many people today that was badly damaged in a fire in 1992 and towed up the Golden Horn to make way for the modern bridge now in use.

Today
Detail of the break in the overhead lines for the trams between one bascule (left) and the fixed part of the bridge. The Süleymaniye Mosque is in the background.

The fifth Galata bridge was built by the Turkish construction company STFA just a few meters away from the previous bridge, between Karaköy and Eminönü, and completed in December 1994. It was designed and supervised by GAMB (Göncer Ayalp Engineering Company). It is a bascule bridge, which is 490 m long with a main span of 80 m. The deck of the bridge is 42 m wide and has three vehicular lanes and one walkway in each direction. It has also recently had tram tracks added to it, allowing the Istanbul Tram to run from Zeytinburnu in the suburbs near Atatürk International Airport to Kabataş, a few blocks before Dolmabahçe Palace. This bridge, Trowse Bridge in Norwich, and a number of rail bridges in the United States may be the only movable bridges in the world which also carry electrified rail tracks.

It is a common argument that the bridge was not designed for this modification, which was added later as a necessity. Laymen had to make inspections of the bridge due to several engineering problems, which caused a setback of many years because of the discord between the supervisor and the contractor. The rest of the bridge including the market area in the first floor opened to common use in 2003.

 

( source : http://en.wikipedia.org/wiki/Galata_Bridge )