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The writer argues his book and the subsequent film illustrates how the ancient, secretive ritual in the Sistine Chapel is a "rather brilliant device" for finding the right person to lead an organisation.

As viewers of the film will know, the papal conclave will take place entirely behind the closed doors of the Sistine Chapel, beneath its world-famous Michelangelo frescoes.

The closed-door meeting will start inside the Sistine Chapel on 7 May and will involve some 135 cardinals from across the world.

Vatican spokesman Matteo Bruni said cardinals will take part in a solemn mass at St Peter's Basilica, after which those eligible to vote will gather in the Sistine Chapel for the secretive ballot.

Once they enter the Sistine Chapel, cardinals must have no communication with the outside world until a new Pope is elected.