For 600 years it was taken that once appointed, the position was for life.
The door had closed, the mobile had central-locked and the Vatican would be the last stop on the way to the Almighty.
But Pope Benedict XVI has decided to mix things up a bit:
From 28 February 2013, at 20.00 hours the see of Rome, the see of Saint Peter, will be vacant and a conclave to elect the new supreme pontiff will have to be convoked by those whose competence it is.
The decision has been inscrutable, so in the absence of reason, let us speculate: