It took 30 hours to winch Big Ben into the tower's belfry
A giant birthday message has been projected on to Parliament's clock tower to mark 150 years since the first ringing of Big Ben.
The Great Bell struck its first hour on 11 July 1859 and a year of celebrations is taking place for the anniversary.
The message reading "Happy Birthday Big Ben, 150 years, 1859 - 2009," was beamed on to the tower after sunset.
Other activities celebrating Big Ben have been organised by the Guy Fox History Project charity.
Over the next 12 months children and volunteers will explore the clock tower and research its history.
After 150 years, Big Ben still holds a special place in the hearts of Londoners and the world
Mike McCann Keeper of the Great Clock
The clock tower at the Palace of Westminster was completed in 1859 and quickly became the most recognisable part of architect Charles Barry's building, which replaced the old Parliament after it burned down in 1834.
But the bell itself has at times had a troubled history.
The first bell cracked under testing two years before the tower was built and its replacement only lasted two months before it also cracked.
For the following four years Big Ben remained silent until repairs and modifications were made.
Since then, it has been damaged by such diverse elements as the weather, workmen and birds, but remains one of the most famous symbols of the UK.
Mike McCann, Keeper of the Great Clock, said: "After 150 years, Big Ben still holds a special place in the hearts of Londoners and the world as a magnificent example of engineering and building genius."
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