Pope Benedict XVI has officially resigned, saying that he now “will simply be a pilgrim” starting his last journey on earth.

Pope Benedict XVI left Vatican City Thursday for the last time as leader of the billion-member Roman Catholic Church, heading by helicopter to his summer residence where he spent the last hours of his pontificate before stepping down.

When he arrives at Castel Gandolfo, the papal summer palace overlooking Lake Albano south of Rome, the pope is expected to greet a crowd of faithful and the local parish priest.

Then, at 8 p.m., the pope’s resignation – the first of its kind in six centuries – took effect.

Earlier in the day Pope Benedict XVI vowed “unconditional obedience and reverence” to his eventual successor.

He was speaking on his final day in office at the Vatican to his cardinals, one of whom will be elected next month to replace him.

“I will continue to serve you in prayer, in particular in the coming days” as the cardinals work to select a new pontiff, he said.

Benedict told the cardinals it was a “joy to walk with you” during his eight years as pope.

Vatican spokesman the Rev. Thomas Roscia said 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 those eligible to vote were present, said Vatican spokesman the Rev. Federico Lombardi.

The final number of cardinal-electors has not been confirmed but is thought to be 115.