The world's busiest metro

By Patrick Jackson BBC News Online

The bomb on the Moscow Metro on 6 February struck at the very heart of this vibrant city of about 9 million souls where a trip "na Metro" is part of everyday life for most.

The Metro provides by the far the handiest way to get around Moscow

It is the busiest underground railway in the world, recording about 9 million passenger rides per day compared with 8 million for Tokyo and 3 million for London.

The network was planned in Soviet times but its relatively cheap fares and extensive network mean that despite Russia's boom in private car ownership over the last decade the Metro is as busy as ever.

And with nightmarish traffic jams now a daily feature on the streets above, people from every walk of life still descend into the Metro where the punctuality and sheer quantity of trains hurtling through the tunnels is the envy of a congested network like the Tube in London.

THE MOSCOW METRO 265.4 km of track, 11 lines and 163 stations Efficient, cheap means of transport for millions every day Tourist attraction in its own right with a tradition of grand, monumental stations Data from Moscow Metro website

Friday's explosion occurred on one of the busiest lines, the Zamoskvoretskaya ("Moscow River"), more familiar to travellers as the green diagonal line on the map linking the city's two main airports - Sheremetyevo in the north and Domodedovo in the south.

It is a line which passes right through the heart of the city, with stations for Red Square and the Bolshoy just a few stops away from where the bomb went off.

The attack happened between Paveletskaya, which serves a rail terminal of the same name and a smart business district, and Avtozavodskaya, named after a nearby car factory.

From bomb shelter to target

Just a few years after the Metro was opened in 1935, its elegant stations - some of the deepest in the world - were serving as shelters from German bombs during the Second World War.

Many Russians associate terrorism with the collapse of the USSR, with its police state securities, and the ethnic conflicts which then erupted, of which Chechnya has been the bloodiest.

However, the first known terror attack inside the Metro itself came during the Brezhnev years, on 8 January 1977, when a bomb planted in a carriage by Armenian separatists killed seven people and injured another 37.

Before Friday's explosion which claimed at least 39 lives, there were four other bomb attacks on the Metro, none of which has been linked conclusively to a particular group:

• In June 1996, a bomb on the Serpukhovskaya Line killed four and injured 12

• In January 1998, a bomb injured three people at Tretyakovskaya Station

• Thirteen people were killed and 118 injured by a bomb in a pedestrian tunnel leading to Tverskaya Station in August 2000

• In February 2001, an explosion injured 20 inside Belorusskaya Station

The one thing which impresses first-time users of the Moscow Metro is the amount of security there appears to be - from the uniformed monitors posted by the escalators to the policemen checking ID cards of passengers with bulky luggage at random in the aisles.

But in the rush hour of a winter's morning in Moscow, where heavy coats are the rule and many passengers would be carrying luggage, it would have been relatively easy for a determined bomber to pass through the ticket barrier and into the stream of humanity heading for the trains.