Ailing: The 85-year-old Pontiff said his strength was 'no longer adequate to continue in office due to his age'
Sense of incredilty: Pope Benedict XVI attends a consistory with cardinals, who were shocked by the decision
GREGORY XII, THE LAST POPE TO RESIGN IN 1415
Pope Gregory XII was the last pope to resign, standing down in 1415.
His resignation ended the Western Schism when different branches of the Catholic church claimed supremacy from 1378 until 1417.
Initially there were two rival popes, each with their own following, cardinals and administrative offices, according to Encyclopaedia Britannica.
The problem arose following the death of Gregory XI, an Avignon Pope.
When the College of Cardinals met to vote for a new pope a Roman mob broke into the voting chamber and forced the election of an Italian pope - Urban VI.
Unhappy with being cornered, some cardinals returned to Avignon where they elected Clement VII as the pope.
This forced followers in Europe to choose allegiance between Avignon and Rome.
Until 1409 there were two popes simultaneously, although the Avignon Popes (Clement VII and then Benedict XIII) were seen as antipopes.
The Roman popes were Urban VI, Boniface IX, Innocent VII and Gregory XII.
Cardinals allied to Gregory XII and Benedict XIII decided to try and resolve the situation by getting the pope and antipope to meet and make an agreement.
However, at the last minute they pulled out and it was decided at a church council in Pisa that they would elect another pope - Alexander V.
He died shortly after being elected and was succeeded by John XXIII.
To resolve the situation the Council of Constance managed to get Pope Gregory and Antipope John to resign so a new election could take place.
As he refused to step down, Avignon Pope Benedict XIII was excommunicated and his successor, Antipope Clement VIII resigned in 1429 in recognition of the Roman Pope Martin V's legitimacy to the papal throne.
Speaking in on of the Vatican's state rooms, the Pope today told cardinals: '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 by 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 barque 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 fulfill the ministry entrusted to me.'
Benedict, who was known as 'God's rottweiler' before becoming Pope because of his stern stand on theological issues, said he was making the decision in 'full freedom' but was 'fully aware of the gravity of this gesture'.
A cardinal who was at the meeting said: ‘We listened with a sense of incredulity as His Holiness told us of his decision to step down from the church that he so loves.’
A Vatican spokesman said he will officially retire at 8pm Rome time (7pm GMT) on February 28.
Benedict will then retire to the Pope's summer residence near Rome before returning to the Vatican to spend the rest of his life in cloistered accommodation.
As he begins his retirement, cardinals in Rome will begin the process of choosing a successor.
Although the Pope's announcement this morning came as a huge shock to his colleagues, there have been rumours about his health since 2011.
The Pope, who has appeared increasingly frail and walking with a cane, is understood to be suffering from a degenerative joint disease.
In November 2011, Andrea Tornielli – a well-placed reporter from the Vatican Insider, a project run by La Stampa newspaper in Italy – said Pope Benedict found it agonising to walk even short distances due to 'arthrosis', thought to be an Italian term for osteoarthritis, in his knees, hips and ankles.
Mr Tornielli said this was why the Pope began using a moving platform to address crowds during mass in St Peter’s Basilica.
The Vatican revealed that he had suffered a mild stroke shortly after being elected Pope and there were unconfirmed reports that he had suffered an earlier one in the early 1990s when he was a Cardinal.
There have also been reports that the Pope was struggling to read texts.
Benedict has previously stated that Popes who are unable to do their job because of ill health should step down.
Benedict's deterioration during the last few months has been particularly noticeable and, according to his brother, he has been considering stepping down for some time.
Georg Ratzinger, who still lives in the family's native Germany, said he had been having trouble walking and his age was weighing on him.
'At this age my brother wants more rest,' he said adding that the doctor had warned him not to take any more transatlantic trips.
Despite Benedict being open with his family, he appears to have said little to cardinals and staff at the Vatican about his ailing health.
In a hastily arranged and, at times, shambolic press conference this morning, Vatican spokesman Federico Lombardi said: 'It’s taken us a bit by surprise. We’ve had to organise ourselves very quickly.
‘We’ve had no warning of what the Pope was about to announce. The declaration is crystal clear and we need to go through it word by word.
Aware of gravity of announcement: Pope Benedict said he had repeatedly examined his conscience before God
Highly unusual move: The Pope is the first to stand down in the last 600 years
‘The Pope says that he looked in a personal way and had a deep moment of reflection to consider the mission that he had received from God.’
The decision to resign is highly unusual as the vast majority of incumbents die in office. He is the first pope to resign in 600 years.
Cardinal Joseph Ratzinger became Pope Benedict XVI when he took office at the age of 78 in April 2005.
He succeeded Pope John Paul II, continued serving right up until his death despite suffering a number of health problems including cancer, osteoporosis and Parkinson's disease.
He also survived two assassination attempts, one of which left him severely injured.
Pope Benedict XVI's election was not without controversy. He was viewed as a deeply conservative man who had headed up the Church's modern-day Inquisition.
He was also served in Hitler Youth during World War Two. Although membership was compulsory at the time, the issue dogged him through the early years of his papacy.
However, once he took office he gained a reputation as a charming and shy man who won over many of his critics.
He was only the second non-Italian Pope since 1522 and the oldest on election since the 18th century.
He said after he was elected to the Papacy that he had prayed not to get the post and was hoping for a peaceful old age.
As the powerful Cardinal Joseph Ratzinger, he was already well-known within the Catholic world before his election to the top job.
His image on elevation to the Papacy was one of an enforcer of Catholic orthodoxy and a cerebral disciplinarian who was unafraid to crack down on liberals and dissidents within the church.
Pope Benedict XVI is to stand down as leader of the Catholic church, it was announced today
Pope Benedict XVI meets members of the Order of the Knights of Malta after the Mass to mark the 900th anniversary of the Order in Vatican City on Saturday. He said his health is too weak to continue in office
CONCLAVE AND SMOKES SIGNALS: HOW THE CATHOLIC CHURCH ELECTS A POPE
Roman Catholic cardinals seeking a successor to Pope Benedict XVI will hold a conclave to elect a new pontiff.
Only cardinals are eligible to take part in the conclave, which will continue until a successor is chosen.
The cardinals will meet in the Vatican's ornate Sistine Chapel and hold two voting rounds a day until they choose a new pope with a two-thirds majority.
They were traditionally locked into the Chapel, best known for the frescoed ceiling and altar wall painted by Michelangelo, and not allowed out until they chose a new pontiff.
They had to sleep in makeshift cells and share minimal sanitary facilities.
But new regulations issued by Pope John Paul II in 1996 allow them to live in a new hotel built on Vatican grounds behind St. Peter's Basilica and even take walks in the tiny state's peaceful gardens between their voting rounds.
Another reform lets the cardinals opt for a simple majority vote if they have not succeeded in electing a pope after about two weeks of balloting.
Most modern conclaves have lasted only a few days.
When the cardinals are in agreement, the chosen one will say 'Accepto,' a puff of white smoke, above, will emerge from the chimney, bells will toll and a cardinal will appear at the central window of St Peter's Basilica to declare 'Habemus papam' - 'We have a pope'.
While Prefect of the Congregation for the Doctrine of the Faith (CDF), he gained the nickname 'God's Rottweiler' for his pursuit of Catholic theologians and clergy seen to stray from orthodox teaching.
His pronouncements before becoming Pope included labelling homosexuality a 'more or less strong tendency ordered toward an intrinsic moral evil' and saying rock music could be a 'vehicle of anti-religion'.
The Pope has also proved himself to be strongly against the ordination of women as priests, euthanasia, abortion and the use of artificial birth control.
Since his election as Pontiff his image has softened, leading him to be dubbed 'Benedict the Benign' in some quarters - but he has also attracted considerable controversy.
The Pope's 2009 visit to Africa was overshadowed by a row sparked by comments he made while flying to the continent in which he rejected condoms in the fight against Aids.
His decision in 2009 to lift the ex-communication on renegade English cleric Richard Williamson, who made comments suggesting only 200,000 to 300,000 Jews died in the Holocaust and none perished in gas chambers, also caused uproar.
The Pope later issued a letter expressing his regret about the damage the affair caused to relations with the Jewish community, saying he had not known about Williamson's stance on the Holocaust when he took the decision to lift the ex-communication.
Perhaps his biggest setback as Pope was during his visit to Germany in 2006 when he was caught in a firestorm of criticism from the Islamic world after giving a lecture at his old university of Regensburg.
Quoting from an obscure Medieval text, he cited the words of a Byzantine emperor who characterised some of the teachings of the Prophet Mohammed, Islam's founder, as 'evil and inhuman' - remarks that touched off widespread anger across the Muslim world.
The anger and violence sparked by his comments including attacks on seven churches in the West Bank and Gaza posed one of the biggest international crises involving the Vatican in decades.
In Somalia, gunmen killed an Italian nun and her bodyguard at the entrance of a hospital where she worked, in an attack that some feared was linked to the outrage over the Pope's remarks.
Pope Benedict XVI (left) during a service in Saint Peter's Basilica to mark 900th anniversary of the Order in Vatican City
Pope Benedict XVI waves to pilgrims while standing on the balcony of St Peter's Basilica, Vatican City after being elected in April 2005
He later apologised, saying he was 'deeply sorry' about the angry reaction to his remarks about Islam and holy war, saying the text he quoted did not reflect his personal opinion.
The Pope was made Archbishop of Munich and Freising in 1977 after a career as a university professor.
He was born in the village of Marktl am Inn in Bavaria - he explained on a visit to Germany after his election 'my heart beats Bavarian'.
His formative years coincided with the lifespan of the Third Reich. His family opposed National Socialism but did not participate in public resistance to the Nazis.
GHANAIAN CARDINAL IS BOOKIES' FAVOURITE TO BECOME THE NEXT POPE
Within minutes of Pope Benedict's announcement, speculation was rife about who would replace him.
There are several papal contenders in the wings, but no obvious front-runner - the same situation when Benedict was elected pontiff in 2005 after the death of Pope John Paul II.
However, cardinal Peter Kodwo Appiah Turkson has emerged as the early favourite, with Paddy Power offering odds of 5/2, closely followed by Canadian Marc Ouellet at 3/1.
Here, MailOnline looks those in contention, their odds and some of their strongly held beliefs.
9/4 Cardinal Peter Kodwo Appiah Turkson, pictured right, 64
Country: Ghana Cardinal in the Ghanaian Catholic Church
Elevated to cardlinalate by Pope John Paul II
Significant views: Would like to see a black pope. Believes condoms should be used in marriage if one partner is infected with Aids.
5/2 Cardinal Marc Ouellet, 68
5/2 Cardinal Marc Ouellet, 68
Country: Canada
Elevated to the cardinalate by Pope John Paul II
Significant views: Belief that abortion is unjustifiable, even in cases of rape.
7/2 Cardinal Francis Arinze, 80
7/2 Cardinal Francis Arinze, 80
Country: Nigeria
Elevated to cardlinalate by Pope John Paul II
Significant views: Extreme conservatism on birth control and abortion
7/1 Archbishop Angelo Scola, 71
7/1 Archbishop Angelo Scola, 71
Country: Italy
Elevated to become Archbishop of Milan by Benedict XVI
Significant views: Wants to work more closely with Islam and support Christians in the Middle East
10/1 Cardinal Oscar Rodriguez Maradiaga, 70
10/1 Cardinal Oscar Rodriguez Maradiaga, 70
Country: Honduras
Elevated to cardinalate by Pope John Paul II
Significant views: A moderate but is anti-abortion and criticised Ricky Martin for using a surrogate mother
12/1 Cardinal Tarcisio Bertone, 78
Country: Italy
Elevated to cardinalate by Pope John Paul II
Significant views: Blamed homosexual infiltration of the clergy for Catholic child sex scandals
14/1 Cardinal Angelo Bagnasco, 70
14/1 Cardinal Angelo Bagnasco, 70
Country: Italy
Elevated to cardinalate by Pope Benedict XVI
Significant views: Strongly against abortion and expressed anger towards same-sex unions
16/1 Cardinal Jorge Mario Bergoglio, 77
Country: Argentina
Elevated to cardinalate by John Paul II
Significant views: Against abortion and euthanasia, is against same-sex marriage but calls for respect of gay people. Washed the feet of 12 Aids patients in 2001.
20/1 Cardinal Leonardo Sandri, 69
Country: Argentina
Elevated to cardinalate by Benedict XVI
Significant views: Said Christians in Iraq under Saddam Hussein were more free than they are now
25/1 Cardinal Christoph von Schonborn, 68
25/1 Cardinal Christoph von Schonborn, 68
Country: Austria
Elevated to cardinalate by John Paul II
Significant views: Said use of a condom by an Aids sufferer could be seen as a 'lesser evil'.
50/1 Archbishop Vincent Nichols
Country: England and Wales
Appointed as Archbishop of Westminster in April 2009
Significant views: Tried to exempt Catholic adoption agencies from placing children with gay people but appears more accepting of homosexuality
He was forced against his will into Hitler Youth at the age of 14 and into the Wehrmacht at 16, serving in an anti-aircraft unit before deserting towards the end of the war.
He was once viewed as a progressive within the Catholic Church and played a key role in the reforming Vatican II, the meeting between 1963 and 1965 that introduced sweeping reforms to the church.
It is believed that his experience of Marxist unrest amongst students in the theology faculty in Tubingen, southern Germany, in 1968 where he was a professor contributed to his conservative outlook.
In private, the Pope is known to be an accomplished pianist and a lover of Mozart.
He is also a cat lover and, as Cardinal Ratzinger, was known to have looked after stray cats in Rome.
He is also a cat lover and, as Cardinal Ratzinger, was known to have looked after stray cats in Rome.
POPE BENEDICT'S RESIGNATION STATEMENT IN FULL
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.
