AROUND 140,000 people crowded into St Peter’s Square to hear Pope Francis deliver Christmas mass today, Christmas day. Rome, and by extension Europe, has been the centre of Christianity ever since Emperor Constantine converted to Christianity some 300 years after, according to Christian tradition, Peter, the first pope, arrived there from the Holy Land to spread the gospel and was later crucified. Two millennia later, Christianity is the world’s most popular religion—there are 30% more self-identified Christians in the world than Muslims—and Europe is still the continent with the largest Christian population.