VATICAN CITY -- Pope Benedict XVI has left Vatican City for the last time as pontiff. He emerged late in the afternoon from the Apostolic Palace, walking with the help of a cane, for a short car ride to a waiting helicopter that would then fly him into retirement.

CBS News correspondent Mark Phillips said the crowd outside the Palace was large, but not huge, perhaps because Benedict failed to ever garner the sort of public adoration that his predecessor Pope John Paul II did, or perhaps because many of those wishing to bid Benedict farewell did so the previous day during his last general audience at St. Peter's Square.

CBS News is broadcasting a Special Report with live coverage of Benedict's arrival at Castel Gandolfo, which can also be seen live on CBSNews.com.

After the papal limousine wound its way to the highest point in the Vatican gardens, on which the helipad sits, Benedict and a few of his closest aides boarded the Italian Air Force helicopter for the short flight to the town of Castel Gandolfo. The sun was just beginning to set over the Roman skyline as the helicopter's rotors started to spin, and the Vatican bells chimed.

As his helicopter took off, the final tweet on the Pope's official account, @Pontifex, was issued:

The account was to be shut down after that, his 39th tweet.

Benedict made the short flighty by helicopter from the Vatican gardens to the papal retreat at Castel Gandolfo, just minutes by air to the south of Rome. He emerged minutes after arriving on a balcony overlooking a square below the residence, which has been used by pontiffs to escape the heat of Rome for centuries.

"Thank you for your friendship, for your affection," said Benedict, in what would likely be his last appearance as pontiff in public. He vowed to continue serving the Church in his retirement, saying "we will proceed forward for the good of the Church, for the good of the world... Thank you and good night, to everyone, thank you."

With that, he turned and walked back into the sprawling complex.

Benedict is expected to spend about two months at the private retreat, surrounded by 135 acres of picturesque, private gardens, before moving into an apartment still being prepared in a convent within the Vatican campus walls.

At Castel Gandolfo, at 8 p.m. (2 p.m. Eastern) — the exact moment Benedict's resignation goes into effect — the doors of the palazzo will close and the Swiss Guards in attendance will go off duty, their service protecting the pope now finished. As CBS News correspondent Allen Pizzey notes, however, even a former pope remains a potential target, and the duty of his protection will henceforth be carried out by Vatican police.

Much speculation has surrounded the date when the conclave will begin for the cardinals to chose a new pope. On Thursday, soon after Benedict left the Vatican, Monsignor Carlo Maria Celli, a papal communications officer, hinted that the date could be March 11. That could not be immediately confirmed.

He then gave a blessing, and personally greeted each of the cardinals in attendance, shaking their hands and exchanging a few words as they approached him in turn. The Vatican said he spent the hours before his departure having lunch and resting

Benedict thanked the estimated 150,000 thousand people gathered before him, and said he was "fully aware" of the seriousness and novelty of the situation his retirement had presented the Catholic world.

Many of the cardinals -- the so-called princes of the Church -- who will soon be tasked with choosing Benedict's successor were in the square to hear him speak.

Pizzey says Benedict described the job that his replacement will inherit as being like a ship tossed on stormy seas, a clear acknowledgement of the difficulties he has faced during his near-eight-year papacy. He went so far as to say that, at times, it seemed like "the Lord was sleeping."

From the point when the doors of Castel Gandolfo close behind him on Thursday, the Vatican says Pope Benedict XVI -- who will be known in his retirement as Pope Emeritus -- will essentially shrink away into a quiet life of prayer and meditation.

However, Pizzey notes that while Benedict will be banned from making public statements in his retirement, it is widely expected that his successor may take advantage of having someone nearby with whom to consult on the job at hand.