Pope Benedict attends a celebration for his 85th birthday at the Vatican April 16 2012.
A year and a half ago, Pope Benedict began riding a mobile platform in liturgical processions to ease the burden of those processions.
Just a few months later, the pope began using a cane to walk, although it often looks like he is carrying it, not relying on it, for support.
However, just in the past few months when celebrating Mass in St. Peter's Basilica, the pope no longer walks around the altar when using incense at the beginning of Mass; instead he raises the thurible only from the back of the altar.
And at the end of a Mass Feb. 2, the pope lost his grip on his crosier; as it fell, Msgr. Guido Marini, the papal master of liturgical ceremonies, caught it.
All these were signs of Pope Benedict's increasing frailty, a frailty that led him to conclude he no longer has the strength to carry out his ministry as pope.
On Feb. 11, the pope announced that he will resign Feb. 28 after a nearly eight-year pontificate.
"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 cardinals gathered for an ordinary public consistory to approve the canonization of new saints.
Pope Benedict will be the first pope to resign since 1415.
In today's world, he told the cardinals, the pope needs both strength of mind and strength of body to govern the barque of Peter and proclaim the Gospel.
In the last few months, that strength "has deteriorated in me to the extent that I have had to recognize my incapacity to adequately fulfill the ministry entrusted to me," he said.
The pope said he will now serve the Church through a life devoted to prayer.
Jesuit Father Lombardi, Vatican spokesman, told journalists that although the announcement had caught almost everybody by surprise, it was not a snap decision, but rather one that "had matured over the past few months."
Lombardi said after the pope steps down, he will move to the papal villa in Castel Gandolfo. After renovations are completed at the Mater Ecclesia monastery, located inside the Vatican Gardens, the pope will move there and dedicate his time to prayer and reflection.
The Jesuit said a sede vacante usually lasts less than a month, and that it was more than likely a new pope would be elected in time to lead the full schedule of Holy Week and Easter liturgies.
Lombardi said being a pope today is "much more fast-moving, more demanding" than it was in the past with an almost nonstop full schedule of public and private events and liturgical celebrations.
Pope Benedict had long said it would be appropriate for a pope to resign for the good of the Church if the pontiff felt he were unable to physically bear the burden of the papacy.
In his book-length interview, The Light of the World, with German journalist Peter Seewald, the pope said, "If a pope clearly realizes that he is no longer physically, psychologically and spiritually capable of handling the duties of his office, then he has a right and, under some circumstances, also an obligation to resign."