VATICAN CITY — The decision, delivered in Latin and in unemotional tones by Pope Benedict XVI to a gathering of cardinals on Monday, came “like a bolt out of the blue,” one of the participants said, and it soon ricocheted around the world.

During what was supposed to be a routine meeting to discuss the canonization of three potential saints, Benedict read a statement that said, in part, that after examining his 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 leading the world’s one billion Roman Catholics. He was resigning on Feb. 28, he said, becoming the first pope to do so in six centuries.

“In today’s world,” Benedict said in his announcement, “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 St. 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.”

Within minutes, #Pontifexit was trending on Twitter. Later, during an evening thunderstorm, a lightning bolt struck the dome of St. Peter’s, though the meaning, if any, was not immediately clear.