A Pope had not resigned for almost 600 years until yesterday's announcement.

There is a tradition and belief that the position is for life.

But though unorthodox, there is a precedent within history for a Pope to step down voluntarily, and even a legal framework within canon law.

The only conditions that have to be met are that the Catholic Church's leader leaves his position "freely", and that his reasons for doing so are properly published.

This explains why Pope Benedict XVI said: "with full freedom I declare that I renounce the ministry of Bishop of Rome".

In modern times it was revealed in 2005 that Pope John Paul II had considered resigning five years previously, when he was 80, before turning against the idea.

But the last Pope to resign was Pope Gregory XII, who reigned from 1406 to 1415 during a time known as the Western Schism which saw three rivals claim the papal throne.

Roman Pope Gregory XII, who was in dispute with the Avignon Pope Benedict XIII, and the Antipope John XXIII formally con- vened a Church Council and authorised it to elect his successor.

He then retired and lived the rest of his life in peaceful obscurity.

Other popes have also left office while still living – although the decision was not always their own.

Martin I, pope from 649-655, died in prison after he was exiled by the emperor Constans II, while Benedict V was forced to stand down by Holy Roman Emperor Otto I in 964 in favour of a more pliable candidate.

And in 1294, Pope Celestine V issued a solemn decree declaring it permissible for a pope to resign only five months after his election.

He then did so, going off to live as a pious hermit.