Pope Benedict XVI surprised the world with his announcement Monday that he would resign at the end of February.

The first pontiff to leave his post in nearly 600 years, the decision sets the stage for a conclave to elect a new pope before the end of March.

The 85-year-old pope announced his decision in Latin during a meeting of Vatican cardinals to name three new saints Monday morning.

"After having repeatedly examined my conscience before God, I have come to the certainty that my strengths due to an advanced age are no longer suited to an adequate exercise of the Petrine ministry," he told the cardinals.

The pope added: “In order to govern the bark of St. Peter and proclaim the Gospel, both strength of mind and body are necessary — strengths which in the last few months, has deteriorated in me to the extent that I have had to recognize my incapacity to adequately the ministry entrusted to me."

The last pope to resign was Pope Gregory XII, who stepped down in 1415 in a deal to end the Great Western Schism among competing papal claimants.

Benedict called his choice "a decision of great importance for the life of the church." He had been on the job since 2005.

The move sets the stage for the Vatican to hold a conclave to elect a new pope by mid-March, since the traditional mourning time that would follow the death of a pope doesn't have to be observed.

There are several papal contenders in the wings, but no obvious front-runner as was the case when Benedict was elected pontiff in 2005 after the death of Pope John Paul II.

After having repeatedly examined my conscience before God, I have come to the certainty that my strengths, due to an advanced age, are no longer suited to an adequate exercise of the Petrine ministry.
— Pope Benedict XVI

According to the pope's brother, Georg Ratzinger, the pontiff had been advised by his doctor not to take any more transatlantic trips and had been considering stepping down for months.

Talking from his home in Regensburg to the news agency dpa, Ratzinger said his brother was having increasing difficulty walking and that his resignation was part of a "natural process."

"His age is weighing on him," the 89-year-old said of his 85-year-old brother. "At this age my brother wants more rest."

Speculation first arose that the pope could possibly resign in April of last year.

"I am facing the final leg of the path of my life and I don't know what's ahead," Benedict said during his 85th birthday celebration. "I know though that God's light is there ... and that his light is stronger than every darkness."

Here's the full text of the Pope’s resignation announcement:

"Dear Brothers,

I have convoked you to this Consistory, not only for the three canonizations, but also to communicate to you a decision of great importance for the life of the Church. After having repeatedly examined my conscience before God, I have come to the certainty that my strengths, due to an advanced age, are no longer suited to an adequate exercise of the Petrine ministry. I am well aware that this ministry, due to its essential spiritual nature, must be carried out not only with words and deeds, but no less with prayer and suffering. However, in today's world, subject to so many rapid changes and shaken by questions of deep relevance for the life of faith, in order to govern the bark of Saint Peter and proclaim the Gospel, both strength of mind and body are necessary, strength which in the last few months, has deteriorated in me to the extent that I have had to recognize my incapacity to adequately fulfill the ministry entrusted to me. For this reason, and well aware of the seriousness of this act, with full freedom I declare that I renounce the ministry of Bishop of Rome, Successor of Saint Peter, entrusted to me by the Cardinals on 19 April 2005, in such a way, that as from 28 February 2013, at 20:00 hours, the See of Rome, the See of Saint Peter, will be vacant and a Conclave to elect the new Supreme Pontiff will have to be convoked by those whose competence it is.

Dear Brothers, I thank you most sincerely for all the love and work with which you have supported me in my ministry and I ask pardon for all my defects. And now, let us entrust the Holy Church to the care of Our Supreme Pastor, Our Lord Jesus Christ, and implore his holy Mother Mary, so that she may assist the Cardinal Fathers with her maternal solicitude, in electing a new Supreme Pontiff. With regard to myself, I wish to also devotedly serve the Holy Church of God in the future through a life dedicated to prayer."

Based on reporting by the Associated Press.