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As Paragone said, this question covers a vast account of the history of London. Briefly, London was born at a point where the Thames could be forded during the first century AD. It's the largest river in Britain fed by streams from Highgate, Hampstead and Camberwell. The Fleet, Tyburn and Westbourne ran into it; the Fleet serving as a foul ditch in later times - there's an engraving showing what it looked like. The City of London began here, and building gradually began to expand westwards. For hundreds of years the old London Bridge crossed it, covered with buildings and built on pontoons. The arches meant that the river was impeded, so boats which were navigated through had to negotiate difficult levels - it could be dangerous. It also meant that it slowed the river down so that it could freeze in winter. Many fairs were held on the ice in past centuries. Because there was only one bridge until the 18th century, one would cross by hiring one of the many boatmen to reach the pleasure gardens or the taverns and pleasures of the south bank. It was also used as a thoroughfare for many years; kings and queens would travel by barge from one palace to another (think Hampton Court and the Tower of London). Many times the Thames was ready for the defence of London; if the Armada sailed up the estuary, it would be faced with a boom across the river at Tilbury. And many ships set sail from there. "To this city, from every nation that is under heaven, merchants rejoice to bring their trade in ships" wrote Fitz Stephen; in warehouses along the eastern part of the Thames were piled wool, cloth and corn, chief sources of England's wealth. There are still warehouses and even underground stations with names associating themselves with the import and export of cloth, coffee, sugar and goods from all over the world, and there are still some old warehouses left. The Thames was a source of life, of wealth, food and a means of travel through the ages, and it still draws people by the great buildings situated on its banks, like the Houses of Parliament.