When Victorian businessmen built the world's first underground railway 150 years ago their ambitions were relatively small.
The plan was to ease the traffic gridlock between West London and the City.
Little did they know that their Metropolitan Railway would change the face of London.
Originally built as a 3.5mile link between Paddington and Farringdon, the line was the catalyst for rapid urban expansion into the Home Counties during the first half of the 20th century.
The previously rural areas northwest of the Capital opened up by the original Underground network became known as Metro-land.
The name was coined in 1915 by the Metropolitan Railway's publicity department, which set up a company to develop housing and shops along the line.
Londoners could escape the crowded city streets and polluted air for a slice of country living within easy reach of the Capital.
From then on, Metro-land was the key word in advertising slogans drawn up to entice workers 'from cramped homes in central London into a rural paradise', where detached houses 'built of the finest materials' could be bought for under £700 (£36,000 in today's money).
Most of Metro-land was developed between the two world wars and its 'new havens' were said to have created a distinctive atmosphere.
However, there were detractors.
Among them were those who said it was wrong for the countryside to be turned into suburbia.
No developer would be allowed such free rein today.
Indeed, the spread of Metro-land helped instigate the Green Belt.
However, following development in the 1960s of prefab tower blocks, suburbia was re-assessed and gained many new supporters who spoke in favour of 'its spacious, leafy pleasures'.
It also became better understood that London's dramatic growth was dependent on the emergence of a modern public transport network, as is the case today with the Capital's population expected to continue rising over the next decade.
London Underground has a well established reputation for outstanding poster design.
The upcoming Poster Art 150 exhibition at the London Transport Museum in Covent Garden will showcase 150 of the best designs, dating right back to the first poster commission in 1908.
The exhibition will run from mid-February to October.
Metropolitan line - oldest and newest
The oldest line on the Tube network now has some of the newest trains.
In 2011, air-conditioned, walk-through carriages were introduced featuring easier access, better audio and the latest visual information systems.
New signalling technology will be installed by 2016, which will mean capacity on the line will increase by 49 per cent.
The work is part of the wider Tube upgrade plan to improve trains and stations, increase capacity and make the network more accessible.