Construction work began Sunday on a 2.5-billion-dollar (2.1-billion-euro) project to build a rail tunnel under the Bosphorus Strait that flows through Turkey's biggest city Istanbul.
Despite fears about the risk of earthquakes, the underwater train tunnel will run 1,600 metres (5,280 feet) at 60 metres below sea-level.
Turkish Prime Minister Recep Tayyip Erdogan and several ministers attended a ceremony here to mark the start of digging. The tunnel is expected to be completed by 2007-2008.
Work is led by a Turkish-Japanese consortium and the cost of the project is being supported by the Japanese Bank for International Co-operation.
Turkey's Transport Minister Binali Yildirim said the tunnel would be able to resist an earthquake measuring up to nine on the Richter scale because it was built into two metres of rock.
Seismologists have warned for years of the possibility of a major quake hitting Istanbul, which is home to 10 million people.
Turkey lies over a fault in the earth's surface running east to west and is frequently shaken by quakes, often with serious consequences. In August 1999, around 20,000 people were killed at several locations in northern Turkey in earthquakes.
Two suspended bridges currently straddle the Bosphorus Strait but struggle to cater for all the city's traffic. Istanbul stands at the southern end of the strategic Bosphorus passage.