Here is an extraordinary statistic. Little more than a century ago there were nine million Christians in Africa. Today the figure stands at roughly half a billion, and 140 million of them are Catholics. This explosion of Christianity has, according to the Nigerian Cardinal John Onaiyekan, been a “miracle of grace”, or, put in more prosaic sociological terms, an incredible feat of evangelisation.

The 73-year-old Archbishop of Abuja was in Rome for a conference on African Christian theology, organised by the University of Notre Dame and designed to get behind the bald growth figures and ask deeper questions about what is going on inside the Church in this continent. The event brought together theologians, opinion formers and some of the “lions” of the African Church, including Francis’ point man on the continent, Democratic Republic of Congo (DRC) Cardinal Laurent Monsengwo, and the influential Cardinal Francis Arinze, former prefect of the Vatican’s liturgy department. Aged 84 and retired, the Nigerian prelate is still remarkably active and his flat just steps away from the colonnades of St Peter’s Square remains a favourite point of contact for bishops visiting Rome.

The gathering was held a stone’s throw from the Colosseum in Notre Dame’s swish “global gateway” centre. Outside in its sunlit courtyard during one of the coffee breaks I was struck by the dynamism of the African Church: groups of young priests and religious sisters mingled and debated while Cardinal Onaiyekan explained that he opens new parishes every month in his archdiocese.