Sitting at the crossroads of Europe and Asia, the ancient city of Istanbul has seen thousands of years of trade, battles and invasions. Now it is the scene of one of the most audacious engineering projects in the world.

The Marmaray Rail Tube Tunnel, due to open in 2010, will not only be the deepest underwater tunnel ever constructed. It willalso pass within 16 kilometres of one of the most active geological faults in the world. A major earthquake is not only expected, but imminent. No wonder the Turkish government is calling it the project of the century.

Istanbul is divided by the Bosporus strait that connects the Black Sea to the north of the city with the Sea of Marmara to the south (see Map). Part of the city lies in Europe, on the western side of the strait, while the rest is in Asia. Two road bridges cross ...