VATICAN CITY: Pope Benedict XVI, who stunned the world on Monday with the announcement he will resign on February 28, is the first pontiff to step down in modern Catholic Church history.

At most, there have been only five papal abdications in 2,000 years, but numerous popes were deposed or exiled, 21 popes are listed as martyrs and nine others are considered martyrs.

Four popes died in exile or in prison, six were assassinated, two died of wounds received in the course of riots and one was killed when a roof collapsed.

Here are some examples of previous popes who have given up the papacy:

-- In 1045, Benedict IX, renowned as one of the most disgraceful popes the Church has known, sold his papacy to his godfather, pious priest John Gratian, so that he could get married. Reportedly unable to persuade the woman in question to have him, he returned to seize Rome.

-- In 1046, Gratian, who had reigned shortly as pope Gregory VI and was considered the true pope by many despite Benedict IX's violent return to claim the throne, was forced to resign himself amid accusations he had bought the papacy.

-- In 1294, Celestine V, a simple hermit who was elected to end a deadlock among cardinals, proved incompetent and stepped down after reigning a mere five months. He had issued a decree declaring it possible for a pope to resign, opening up the way for his own departure.

-- In 1415, Gregory XII resigned in a bid to end the "Western Schism", when two rival claimants declared themselves pope in Pisa and Avignon and threatened to tear apart Roman Catholicism.

-- In 1804, Pius VII signed an abdication of the papal throne before setting out for Paris to crown Napoleon to be put into effect in case he were imprisoned in France.

-- During the Second World War, Pius XII is reported to have signed a document which said that he was to be considered as having resigned his office should he be kidnapped by the Nazis.

Several popes were resigned or martyred as the Roman Empire collapsed, and the Eternal City -- sacked and depopulated by barbarian hordes -- fell prey to quarrelling factions. But the historical details of how they fell are often lost in the mist of time, and often only the legends remain.