Pope Benedict XVI pledged his "unconditional reverence and obedience" to his successor Thursday, then left the Vatican as the first Roman Catholic Church leader to resign in 600 years.

A helicopter took Benedict to Castel Gandolfo, the papal retreat outside Rome, even before his eight-year papacy formally ended at 8 p.m., local time (1900 UTC).

The 85-year-old pontiff said a private farewell earlier to Roman Catholic cardinals inside the Vatican. He urged them to unite, saying "among you there is the future pope" whom they will have to choose in the coming weeks.