VATICAN CITY The papacy of Benedict XVI came to a quiet end at 8 p.m. on Thursday (Feb. 28), making him the first pope in 600 years to voluntarily leave office. While there was no formal ceremony to mark the historic passage, the end of Benedict's papacy and the beginning of the “sede vacante” interim period was clear when the Swiss Guards left their post at the gate of the papal summer residence in Castel Gandolfo.

The Swiss Guards are charged with protecting the pope. When Benedict ceased to be pope, his security was no longer in their hands. At the Vatican, officials sealed the pope's apartment as prescribed by church law, and will destroy the pope's ring and official seal in the coming days.

Benedict's last day in office brought to an end an extraordinary two weeks for a Vatican that is already scrambling to get ready for the election of the new pope.

Almost 150 cardinals were in Rome on Thursday to bid Benedict farewell, while informal consultations and private meetings to discuss his successor are already underway.

Benedict, who will continue to be called “His Holiness” and will have the title of “Pope Emeritus” in retirement, flew by helicopter to Castel Gandolfo at about 5 p.m. local time after bidding his final farewell to the Vatican.

He will return there in a few months to live out his retirement in the small Mater Ecclesiae convent, a few hundred meters away from the Apostolic Palace where his successor will be living.

“Thank you for your love and support. May you always experience the joy that comes from putting Christ at the centre of your lives,” Benedict tweeted as he was leaving the Vatican.

The Vatican explained that the pope's @pontifex Twitter account, which has 3 million users in 9 languages, will be frozen during the “sede vacante,” and the new pope can decide whether to continue using it.

After a final goodbye by staff and other aides in the St. Damaso courtyard, Benedict was driven to the small Vatican helipad where he boarded the helicopter that took him to Castel Gandolfo.

As the sun was setting over Rome, hundreds of people watched from St. Peter's Square and from surrounding rooftops as his helicopter made one last swoop over the Vatican. Bells rang all around the city to mark the event.

From the balcony of the Castel Gandolfo palace, an emotional Benedict greeted a crowd of about 7,000 that had gathered in the small village square.

“Thank you for your friendship and your affection. … You know that this day is different for me than the preceding ones,” he said.

“I am simply a pilgrim beginning the last leg of his pilgrimage on this earth,” he told the crowd before promising to continue to pray and meditate for “the good of the church and of humanity.”

“Blessed be God Almighty, Father, Son, and Holy Spirit. Good night! Thank you all!” he said, before turning his back and disappearing inside the palace.

In his retirement, Benedict said he intends to live “hidden from the world.”

Earlier Thursday, Benedict had promised “unconditional” obedience to his successor during a farewell meeting with cardinals.

“Among you, in the College of Cardinals, there is the future pope, to whom I promise my unconditional reverence and obedience,” he said in the last official act of his pontificate before his resignation.

There are expected to be 115 cardinals who are under age 80 and thus eligible to participate in the conclave to elect the next pope. The start date of the conclave will be decided by the daily cardinals' meetings that govern the church until a new pope is elected. The first meeting is scheduled for Monday (March 4).

In his brief, unannounced address on Thursday morning, the pope also issued a renewed appeal for the church's unity.

The College of Cardinals, he said, is “like an orchestra, where diversity, an expression of the universal church, always contributes to a superior harmony of concord.”

“Let us remain united, dear brothers … in prayer, especially in daily Eucharist, and thus serve the church and all humanity,” he added.

Benedict also promised to pray for the cardinals who will gather in the coming weeks in a closed-door conclave to elect his successor.

The Vatican's chief spokesman, the Rev. Federico Lombardi, stressed that while Benedict was in no way obliged to pledge obedience to his successor, it was a “beautiful gesture” to reaffirm that “he has no intention of interfering” with the action of the future pope.