"When our world has become Christian" is an excellent essay by Paul Veyne, for the public non scholar who is less interested in late antiquity and early Christianity, as current discourse on the Christian identity of Europe and the issues discussed today. In this sense, the trial of Paul Veyne is very valuable, and helps redefine some notions misunderstood and used by media thinkers: religion, christianity, ideology. This contribution of a historian and speak at the public square is useful and shows that the scientist has a role to play in the city. However, one can expect more from Paul Veyne, and this book will surely want to curious readers of truth, beyond political discussions without rigor, to learn more and delve into his masterpiece, the Empire Greco Roman, where his talent and historical science give their fullest.