Following a whistle from darkness, a 19-century steam train pulled into the Moorgate station in London on Sunday evening, spewing a cloud of smoke which filled the air with a smell of gas.

About 250 ticket holders were waiting to embark on a journey to retrace the world's first stretch of underground network from Paddington to Farringdon, as part of the 150th anniversary celebrations of its opening in 1863.

"Underground is a vital part of modern London," said Mike Ashworth, design and heritage manager of the London Underground. "It carries 1.2 billion people a year. Even the logos and maps have become icons. Underground has become an international language in London."

"THRILL"` The vintage train's steam engine was made in 1898 and dubbed as Met Locomotive No. 1, attached to which was the oldest surviving operational Tube carriage -- the Metropolitan Railway Jubilee Carriage 353 built in 1892.

Despite the chilly winter evening, many train enthusiasts gathered at the station to take photos or just have a look at the train.

John Grundon, who traveled from 25 miles away just for the event, waited patiently with his big camera. "I love trains," he said. "I know the old trains were smaller, using coals with smoke inside. I also remember Mom talking about war time underground as shelters."

Actors and actresses, dressed in Victorian costumes, made the scene surreal in modern London. Clive Greenwood from Spectrum Drama, wearing a black uniform and with a baton in hand, said he was a "policeman keeping order for people on the platform."

"There is decoration in the carriages with luxurious seats inside," said Greenwood, adding that he was proud of the heritage of London.

But the most excited were those on board of the train.

"It was quite a thrill," said Neil Osborn, who spent half an hour on the non-stop train from Kensington Olympia to Moorgate.

"You can hear the chug-chug back at the carriages, and smell the smoke. It gives you a sense of how it was 150 years ago," he said.

Although the train was slower than those of today, Osborn said he loved it because it was more comfortable.

London Mayor Boris Johnson, who was also a passenger on the train, described his journey as "extraordinary."

"We had steam coming in through the windows, huge thick clouds of white steam going past and then bits of soot coming through from the engine," he was quoted by BBC as saying.

"You understand all those Victorian novels and the assignations that possibly took place on those velvet seats. It was pure Conan Doyle," Johnson said.

CHANGE

Underground is colloquially known as the Tube in London, maybe because of the circular tube-like tunnels.

It boasts some other "firsts" in the world. It incorporated the first line to use electric trains and had the first escalator ever installed underground.

Traffic congestion became a serious problem in London in the 19th century, when different ideas had been put forward. Omnibus service was introduced but the idea failed due to high fares and inconvenient routes. Railways with glass arcade were believed unrealistic as they were too costly.

When the Metropolitan Line was built, The Times condemned it as a "utopian, hazardous proposition."

However, upon completion of the line, the newspaper changed its tone to hail it as "the great engineering triumph of the day."

The old trains had first, second and third class carriages, and even one especially for ladies. But the experience of traveling didn't sound comfortable.

"The smoke and the sulphur fill the tunnel; all the windows have to be closed. The atmosphere was a mixture of sulphur, coal dust and foul fumes from the gas lamps above," a passenger wrote in his diary about his journey.

In comparison, today's trains are "bigger, cleaner and faster," Grundon said. "We have air-conditioners, and wifi from last year."

SYMBOL

The Underground now serves more than 270 stations on 12 lines in London, and has 402 km of track, 45 percent of which is underground.

Movies and literature boomed its fame around the world, from the romantic encounter of Roy and Myra in a shelter of Waterloo Bridge, to the secret lair of Bond movie Die Another Day. Every day there are visitors looking for Harry Potter's platform 9 3/4, or talking about the masked anarchist's headquarters from V for Vendetta.

Stations impressed passengers with their various designs. In the shopping heaven Bond Street, you can see gift boxes on the wall. At Charing Cross near the National Gallery, murals were famous paintings. Baker Street station was the mecca for crime novel fans, who could pose for photos with pictures of Sherlock Holmes stories.

Even the logo and map became a promise for well-sold mugs, T-shirts and table cloths. According to the London Transport Museum, its revenue could top 2.5 million pounds (about 4 million U.S. dollars) a year, 35 percent of which is contributed by foreign visitors mainly from France, Italy, Spain, Brazil, Mexico and China.

The London Underground is more than a means of transportation, said Osborn, the passenger on the old train. "It is part of people's life."