The papacy is one of precious few institutions in the modern world that does not change very much. It maintains the appearance and traditions of the Church much as it has done since the later days of the Roman Empire. One of those traditions has been that the Pope would serve until death.
Catholics were brought up to believe that the election of a Pope, by a college of cardinals in solemn and prayerful conclave, was done with divine guidance and would end when God willed.
No wonder then the news early yesterday stunned the world. Resignation was thought to be no more an option for an ailing Pope than for Britain's monarch, possibly even less likely since it is a mere 77 years since a royal abdication. Historians had to delve back 600 years, to the Middle Ages, for a papal precedent yesterday.
Pope Benedict's decision has taken his Church by surprise. At 85, he seems no more frail than many ageing pontiffs have been. There were signs of health problems but nothing out of the ordinary for someone of his age and no conjecture about his continued ability to perform the functions of the office.