The Metro provides by the far the handiest way to get around Moscow
The bomb attacks on the Moscow Metro have struck at the very heart of a vibrant city where a trip "na Metro" is part of everyday life for many.
It is one of the most-used underground railways in the world, carrying some 5.5 million passengers a day.
The explosions happened at one of the busiest times of the day, when the network was crammed with commuters heading into work.
With nightmarish traffic jams now a daily feature on the streets above, people from every walk of life 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 blasts brought movement on several city centre roads to a standstill, as emergency vehicles sped victims to hospital and helicopters hovered overhead.
From bomb shelter to target
The Metro was planned in Soviet times but its relatively cheap fares and extensive network mean that, despite Russia's boom in private car ownership in recent years, it is as busy as ever.
THE MOSCOW METRO
300 km of track, 12 lines and 180 stations
Efficient, cheap means of transport for millions every day
Tourist attraction in its own right with a tradition of grand, monumental stations
The system covers most of the Russian capital, and is renowned for socialist realist art displayed in certain stations.
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 World War II.
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.
But prior to Monday's deadly explosions, there had not been a major attack on the Moscow Metro for more than six years:
• In February 2004, a bomb on one of the busiest lines, the Zamoskvoretskaya ("Moscow River"), which links the city's two main airports, killed 40 people
- 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