On January 25, 1959, the newly elected Pope John
XXIII invited 18 cardinals from the Vatican bureaucracy to attend a
service at the Basilica of St Paul Outside the Walls in Rome. He told them he planned to summon a global church council.
The horrified cardinals were speechless, which the Pope mischievously chose to interpret as devout assent, writes Barney Zwartz in The Age.
But, in reality, the Vatican bureaucrats, known as the Curia, were aghast.
The Pope, 77, had been elected purely as a caretaker, but here he was indulging a novel, unpredictable, dangerous and, above all, they believed, unnecessary notion.
In their view it would create ungovernable expectations and might even lead to changes.
And if there were to be changes - always undesirable - then the Curia would manage them without any outside intervention, as they had for centuries.
They regrouped and fought back. If they could not avoid the council, then they would control it. They proposed 10 commissions controlled by Curia members to run the council, which would discuss 70 documents prepared by the Curia. Everything was designed to reinforce the status quo.
But the world's bishops, led by a generation of outstanding European theologians, were in no mood to submit. They simply sidestepped the careful preparation and arranged their own agendas.
The Curia were right to worry. What Pope John unleashed, now known as Vatican II, was the most momentous religious event since Martin Luther launched the Protestant Reformation 450 years earlier.
''It was a revolution,'' says American theologian John Markey. ''It was the most fundamental shift in self-understanding by the church in 1500 years. It is not over yet.''
The winds of change proved more like a tornado, leaving almost nothing untouched. It is difficult for people under 60 to grasp how radical, how wide-ranging and how deep the effects were because they do not remember the church as it was before the council - ''frozen in a time warp'', as Jesuit priest Gerald O'Collins told The Age.
Pope John intended the church to emerge from behind the battlements, lower the drawbridge and engage with the modern world.
The most obvious and visible change for Catholics in the pew was worship in their own language rather than in Latin, with the priest now facing them rather than the altar, plus an affirmation of the role of laypeople.
But there were other profound developments such as a willingness to engage with other churches, even other faiths, a renewed focus on social justice, and a decentralised approach to authority in the church.
Today, as religious culture wars between traditionalists and progressives rack the church in the West, Vatican II has become the key battlefield. Both sides want to define and control the council's legacy.