reigning for only five months, his resignation was known as "the great refusal" and was condemned by the poet Dante in the "Divine Comedy". Gregory XII reluctantly abdicated in 1415 to end a dispute with a rival claimant to the papacy.
Lombardi said Benedict's stepping aside showed "great courage". He ruled out any specific illness or depression and said the decision was made in the last few months "without outside pressure". But the decision was not without controversy.
"This is disconcerting, he is leaving his flock," said Alessandra Mussolini, a parliamentarian who is granddaughter of Italy's wartime dictator. "The pope is not any man. He is the vicar of Christ. He should stay on to the end, go ahead and bear his cross to the end. This is a huge sign of world destabilisation that will weaken the Church."
Cardinal Stanislaw Dziwisz, secretary to the late Pope John Paul, said the former pope had stayed on despite failing health for the last decade of his life as he believed "you cannot come down from the cross."
While the pope had slowed down recently - he started using a cane and a wheeled platform to take him up the long aisle in St Peter's Square - he had given no hint recently that he was considering such a dramatic decision.
Elected in 2005 to succeed the enormously popular John Paul, Benedict never appeared to feel comfortable in the job.
"MIND AND BODY"
In his announcement, the pope told the cardinals that in order to govern "... 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 recognise my incapacity to adequately fulfil the ministry entrusted to me."
Before he was elected pope, the former Cardinal Joseph Ratzinger was known as "God's rottweiler" for his stern stand on theological issues. After a few months, he showed a milder side but he never drew the kind of adulation that had marked the 27-year papacy of his predecessor John Paul.
U.S. President Barack Obama extended prayers to Benedict and best wishes to those who would choose his successor.
German Chancellor Angela Merkel said the pope's decision must be respected if he feels he is too weak to carry out his duties. British Prime Minister David Cameron said: "He will be missed as a spiritual leader to millions."
The Archbishop of Canterbury, leader of the worldwide Anglican communion, said