Transcript for Pope Benedict XVI Retirement Countdown
the window of the papal apartment, where pope benedict is spending his last night at pope. And the mysterious figure looks out on st. Peter's square, before seconds later, those lights go out. Now, only hours until the leaderle of 1 billion catholics steps down and returns to his life outside the spotlight. So, let's begin in st. Peter's square with george stephanopoulos, starting us off. George? Reporter: Diane, history was made here in st. Peter's square today. No one has ever seen a pope say good-bye like this. In just hours, he will take off in a helicopter from behind me in st. Peter's basilica. The swiss guards who protect him wills stand down, but that is tomorrow. Today was about farewell. A farewell both buoyant and subdued. Fitting for a pope of paradox. It was a last glimpse, a last chance to hear his words. Soaking in the cheers, benedict rode in his popemobile, waving, kissing babies. And when he rose tospeak, an ovation. It was a frail man today, a marked difference from the day he began his papacy. Known as god's rod wiler, he's been a leader to defend the church. But his papacy would be challenged. Today, he spoke of joy and sadness. Days of sun and light breezes, when the fishing was abundant. But there were times when the waters were choppy and there were headwinds. Times when he said, it looked as if the lord was sleeping. Among those listening, the cardinals. Those who will decide benedict's successor. I spoke with donald wuerl of washington. How about the chances of an american? Cardinal dolan, o'malley of boston? The conventional wisdom, which I think is correct, is a pope from the superpower would probably have a lot going against him, when he's trying to present a spiritual message to the rest of the world. Reporter: Tomorrow night, benedict will no longer be pope. He will be called pope emeritus, wear simple white, those trademark red shoes, symbolizing the blood of martyrs, designed by prada, replaced by ordinary brown handmade in mexico. Pope benedict's most lasting legacy may well be his decision to leave. A very modern decision from a traditional man. The helicopter I told you about is going to take about a 15-minute ride to castle gandalfo, the pope's summer residence. The pope will remain there until restorations are completed on the vatican convent right here. There the pope will live out his days in prayer and study. In his words, diane, he will be hidden to the world. All right, george, our thanks to you. And, of course, when the pope leaves, it will be up to the cardinals and their vote. And here's one snapshot from a modern pilgrimage. There he was, boston's cardinal o'malley on the plane to rome with a newspaper, wearing his signature simple brown robe. And we were all rewinding this tape today. Seven years ago, take a look. There, sealed with a ribbon, a key turns and a new pope, pope benedict, is shown around his new home. The papal apartment. There are ten rooms, floors of 16th century marble. A libraryrowned with an antique ceiling. And soon, another man will be passing through that door, a pope chosen in the mysterious ritual known as the conclave. Abc's david wright tells us about the ancient vote to come. Reporter: Before the cardinals file into the sistine chapel and lock the doors behind them, technicians will have pulled up the floorboards to install cell phone jamming devices. Violating the secrecy is punishable by excommunication. It is the w3ay of ensuring that the voice that's speaking to the cardinals during the conclave belongs to the holy spirit and to no one else. Reporter: No one knows how long it will take. The shortest conclave lasted just a few hours. The longest, more than three years. In fact, that's why they started locking the doors. In the middle ages, during the plague years, the conclave meeting in the town of viterbo took so long, frustrated people eventually locked the cardinals in to hurry them up. It didn't work, so they tried to starve them out. That didn't work. So, they exposed them to the elements, tearing the roof off the building to let the holy spirit in. Not going to happen in the sistine chapel, where the creaming is michelangelo's masterpiece. These days, the cardinals have rooms in a vatican guest house, but they're still cut off from the outside world for the duration. This is your first conclave, if I am not mistaken. It is. Reporter: Cardinal william levada of san francisco has been told what to expect. I think it's a prayerful atmosphere. Reporter: It is not like a party nominating convention. No, no. It is not like that at all. No rah-rah and hooray for this. Reporter: No big speeches. No campaigning. You can't put yourself forward. Reporter: When the time comes to vote, the cardinals are strongly urged to disguise their handwriting, to avoid any awkwardness later. But make no mistake, ever so quietly, the politicking has already begun. This morning, you could see the cardinals whispering. David wright, abc news, rome. And next here tonight, we
This transcript has been automatically generated and may not be 100% accurate.