Pope Benedict XVI spent his final hours as head of the Roman Catholic Church meeting with his cardinals for the last time.

Speaking from the Vatican's frescoed Clementine Hall, the pontiff pledged his "unconditional reverence and obedience" to whomever they choose to replace him.

The pope added that he would "continue to serve you in prayer, in particular in the coming days," as the cardinals work to choose a successor.

Now the pope heads to a papal retreat south of Rome, where he'll remain for several months before returning to live at the Vatican in a convent.

His retirement formally takes effect this evening.