- All Benedict's tweets are hidden, symbolizing the empty seat at the head of the church
- The Swiss Guards leave as Benedict XVI's papacy comes to a formal end
- "I'm just a pilgrim who is starting the last part of his pilgrimage on this earth," he says
- Benedict pledges his "unconditional obedience" to the new pope
Benedict XVI's time as pope came to a historic end Thursday, as he became the first pontiff in six centuries to resign as leader of the world's Roman Catholics, who now number 1.2 billion.
Torchlit crowds stood before the gates of the Castel Gandolfo residence, waiting to see the Swiss Guards, the soldiers who traditionally protect the pope, salute and close the doors on the stroke of 8 p.m.
The guards' departure from the papal summer home brings Benedict's papacy to a formal end. The protection of Benedict there falls now to Vatican police.
The process of transition to that new pope now begins. Meanwhile, the Catholic Church is without a leader.
Symbolizing that gulf at the top, all Benedict's tweets as @Pontifex have been archived. Instead, the account's Twitter page reads only "Sede Vacante," or empty seat.
Earlier, his final words were given to some 10,000 people who had gathered at Castel Gandolfo to bid him an emotional farewell.
"I am no longer the pope but I am still in the church. I'm just a pilgrim who is starting the last part of his pilgrimage on this earth," he said.
He thanked them for their friendship, on a day "different for me than the preceding ones" -- and indeed almost unprecedented for the Roman Catholic Church.
"I would still -- with my heart, with my love, with my prayers, with my reflection, and with all my inner strength -- like to work for the common good and the good of the church and of humanity," he said.
"I feel very supported by your kindness. Let us go forward with the Lord for the good of the church and the world. Thank you."
Smiling slightly, he made the sign of the cross to bless the crowds and disappeared into the building.
It is likely to be the last time he is seen in public.
Benedict, who will now be known as "pontiff emeritus," will spend the next few weeks at the peaceful, hilltop Castel Gandolfo residence before moving to a small monastery within the Vatican grounds.
The first pope to resign in 598 years, his departure ushers in a period of great uncertainty for the church as the cardinals work to elect the next pontiff.
Pomp and ceremony
Benedict earlier left Vatican City for the last time as pope amid pomp and ceremony.
An honor guard of Swiss Guards lined up to bid him farewell as, looking frail and carrying a cane, he left the papal apartment to applause from senior Vatican officials and staff.
The sound of bells from St. Peter's Basilica chimed across the city of Rome as the helicopter carrying him to Castel Gandolfo looped overhead, passing above landmarks like the Colosseum.
Although Benedict will eventually return to Vatican City to live out his days, he will never again set foot there as pope.
Seals will be placed on the entrance to the pope's Vatican apartment, the Vatican said -- to be removed only when the next pontiff enters.
His symbolic Fisherman's Ring and papal seal will be "destroyed" by means of making scratch marks so that they can no longer be used to seal documents, said Vatican spokesman Federico Lombardi.
Benedict's final tweet, sent at 11 a.m. ET from his @Pontifex account, read: "Thank you for your love and support. May you always experience the joy that comes from putting Christ at the centre of your lives."
The account will remain dormant until the next pope decides whether he wants to use it, the Vatican said.
Benedict entered his final day as pontiff with an unusual act -- a pledge of "unconditional obedience" and respect to whoever takes up the reins after his dramatic resignation later.
His promise came in a last meeting Thursday morning with the cardinals who will pick his successor, almost certainly from within their own ranks.
"I will continue to serve you in prayer, in particular in the coming days, so that you may be touched by the Holy Spirit in the election of a new pope," he said.
His words appeared designed to answer concerns that the presence of a former pontiff might lead to confusion or competing loyalties once the new pope is installed.
Benedict told the cardinals it was a "joy to walk with you" during his nearly eight tumultuous years at the head of all Catholics worldwide.
Another Vatican spokesman, the Rev. Thomas Roscia, said he believed 144 cardinals had attended Benedict XVI's farewell to them as pope. That includes both cardinal-electors, who are under the age of 80, and cardinals who are not eligible to vote for the next pope.
Not all the 115 cardinals eligible to vote were present, Lombardi said.
Two cardinals are suffering ill health, making their attendance uncertain, although arrangements may be made to enable them to vote, Roscia said.
The Vatican has said it wants to have the next pontiff in place in time for the week of services leading up to Easter Sunday on March 31.
A series of meetings to set the timetable for the conclave -- the closed-door assembly to elect a new pope -- will begin early next week, said Lombardi. The cardinals will receive the formal invitation to attend on Friday.
The meetings, known as general congregations, bring together all the cardinals, electors and non-electors, before the conclave begins. They are intended to be an opportunity to reflect on the current state of the church.
In their meeting Thursday morning, the cardinals gave Benedict a standing ovation, and then one by one each met Benedict to say a final few words.
Cardinal Daniel DiNardo of Texas said at a news conference held with fellow U.S. cardinals that it had been "a very moving moment with Pope Benedict."
"There was a note of sadness in saying farewell to this man who has been our spiritual father for the last eight years," said Cardinal Sean O'Malley of Boston.
"At the same time it was very edifying to see how much people love him and respect him."
Cardinal Roger Mahony, the retired archbishop of Los Angeles, tweeted after meeting Benedict that he had asked Benedict to pray for the people of Los Angeles. "He grasped my hand and said 'Yes'!!" Mahony said.
The current Catholic archbishop in Los Angeles earlier this month disciplined Mahony for his mishandling of "painful and brutal" allegations of sexual abuse by priests. Mahony's decision to travel to Rome to take part in the election of the new pope has been controversial because of that.
DiNardo and O'Malley said they would pray for guidance in choosing the new pope.
"I consider it one of the most important activities that I will be engaged in as a priest and a cardinal," said O'Malley, for whom the conclave will be his first.
"I think the discussions that we will have in the congregations will be the most important intellectual preparation that we have -- certainly the spiritual preparation has already begun.
"Our people back home and throughout the world are all praying that we will be guided to be able to choose the very best person to lead us."
Cardinals are forbidden to communicate with the outside world -- now including by Twitter -- during the conclave, held within the Sistine Chapel. There is no Internet access inside Santa Marta, where the cardinals will stay during the conclave, Lombardi said.
Cardinal Gianfranco Ravasi of Italy, tipped as a possible future pope, tweeted Thursday morning that he would be away for a few days.
A number of other cardinals, including Ghanaian Peter Turkson, also considered a frontrunner, and New York's Timothy Dolan are also present on Twitter.
Benedict, who will not be involved in the election, will not get any advance notice of who his successor will be, Roscia said. The pope emeritus will find out who has been elected at the same time as the rest of the world.
Cardinal Javier Lozano Barragan of Mexico, who turned 80 last month and so is not a cardinal-elector, would not be drawn to comment Wednesday on who the next pope might be.
As to whether the cardinals are talking to each other about it now, he told CNN: "There are contacts, of course there are contacts. But what people talk about, who knows?
"There is a saying in Rome: He who enters the conclave as a possible pope comes out a cardinal."
Mired in scandal
Benedict's resignation opens up the prospect of unforeseen opportunities and challenges for the Roman Catholic Church.
Many are wondering whether a new pontiff will choose to lead the church in a different direction -- and can lift it out of the mire of scandal that has bogged down this pope's time in office.
Even as Benedict's final week began, Vatican officials were trying to swat down unsavory claims by Italian publications of an episode involving gay priests, male prostitutes and blackmail. Then the news broke that Benedict had moved up the resignation of a Scottish archbishop linked over the weekend by a British newspaper to inappropriate relationships with priests.
Last year, leaks of secret documents from the pope's private apartment -- which revealed claims of corruption within the Vatican -- prompted a high-profile trial of his butler and a behind-doors investigation by three cardinals.
Their report, its contents known so far only to Benedict, will be handed to his successor to deal with, the Vatican said.
Vatican magistrates may have authorized the tapping of two or three telephone lines during the cardinals' inquiry into the leaks, Lombardi acknowledged Thursday, responding to a report in the Italian weekly magazine Panorama that claimed a large-scale surveillance operation had been run.
Lombardi denied there had been "a massive" operation on the scale reported by the magazine, saying there is "no foundation" for the article. Roscia said that if there was any wiretapping or surveillance, "it's a very small process."
Both spokesmen denied that the operation had been ordered by the three cardinals, saying that if it had happened, it was ordered by magistrates.
At the same time, the church faces continued anger about what many see as its failure to deal with child sex abuse by priests.
So, when Benedict announced on February 11 that he would step down, there was inevitable speculation that his move was in some way linked to the brewing scandals.
Dolan, the most senior Catholic cleric in the United States, told CNN's Christiane Amanpour that there was an urgent need for a recovery and renewal in the church
The new pope won't seek to alter the teachings of the church, but could change the way they are presented, Dolan said.
'The Lord seemed to sleep'
The danger for the Vatican is that the scandals risk overshadowing what others see as Benedict's real legacy to the church: his teaching and writings, including three papal encyclicals.
Proof of the Vatican's irritation came with a stinging statement Saturday complaining of "unverified, unverifiable or completely false news stories," even suggesting the media is trying to influence the election of the next pope.
The constant buffeting by scandal will doubtless also have taken a toll on an 85-year-old man whose interests lie in scholarly study and prayer rather than damage control.
Benedict suggested as much at his final general audience Wednesday, when in front of cheering crowds in St. Peter's Square he spoke of steering the church through sometimes choppy waters.
There had been "many days of sunshine," he said, but also "times when the water was rough ... and the Lord seemed to sleep."
Benedict also called for a renewal of faith, and for the prayers of Catholics around the world both for him and his successor.
Italian iReporter Giovanni Francia was in St. Peter's Square to witness the scene. "There was a good atmosphere, (but) full of the sense we have lost a sort of 'grandfather,'" he said. "Now we are a little more alone."