Transcript for Two Popes to Be Canonized as Saints
We're going to turn to Vatican City, when history will be made when two popes will be made at the same time. And two popes will be up for canization. Reporter: It really is extraordinary. And here on the streets of Rome, a joyful moment. The crowds are building up to 1 million pilgrims expected, to join hundreds of bishops and cardinals and thousands of world leaders, to celebrate the ancient ritual of the canonization of saints, for two that were rock stars of the modern era. The crowds are pouring into the eternal city. Souvenir stands doing brisk business. Up to 1 million pilgrims are expected. There's never been anything like this in the long history of the church. Two popes, one day to remember. Probably the two popes that changed the church the most. These are lives that are recorded. We watched them. And now, they're saints. Reporter: For John Paul ii, it's been a fast track for sainthood. Nine years. So fast, it stirred controversy, especially by victims of sexual abuse by priest, a scandal that deepened during John Paul's papacy. But he towered over his times. His fierce resistance to tyranny, seemed to help end the cold war. Sainthood now, and now it comes. John xxiii, when he pushed for a fresher, more modern catholicism. The calling of the council and his personality. He was a very jovial man. A fat and happy saint. Reporter: Pope Francis is expected to be joined by pope Benedict. That's never happened before. And this whole celebration, a moment of unity for the catholic church. Pope John. John Paul ii, a conservative hero. Pope Francis says it's about faith. Amy? Terry Moran, with the latest from the Vatican.
This transcript has been automatically generated and may not be 100% accurate.