Before the State Opening of Parliament the Yeomen of the Guard search the cellars of the Palace of Westminster. This is to ensure that there is no repeat of the Gunpowder Conspiracy, when Guy Fawkes was arrested in the cellars attempting to blow up the Palace. The Yeomen of the Guard are a military corps founded by Henry VII in 1485 and since then they have been the bodyguards of the monarch, although today their duties are purely ceremonial.
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Yeoman of the Guard (opens a new browser window)