The idea of locking up the cardinals was originally a way of speeding up the election.
In modern times, conclaves have been relatively quick affairs. In the 20th Century, none lasted longer than five days. You have to go back to 1831 to find the last marathon, which lasted 54 days.
But that was quick compared with some earlier conclaves.
The unique system for electing a pope has evolved over centuries. After the death of St Peter, the clergy and people of Rome took it on themselves to choose his successor.
It was a recipe for anarchy and bloodshed. In 366, with the Holy Spirit notably absent, rival mobs massacred their opponents by the hundred.
After the eighth century, the choice was made purely by the Roman clergy... in theory at least. Powerful families continued to influence the election, with money and threats.
In 1059, perhaps in desperation, the job of electing the Pope was handed over to the cardinal bishops.
In 1179, all cardinals were given voting rights, and the two-thirds majority rule was introduced.
Locked up
The practice of locking up the cardinals dates from 1243. The word conclave comes from the Latin to lock up "with a key".
A Roman senator thought that by confining the clerics to a crumbling "palace" at the height of summer, he would encourage them to reach a quick decision.
The squalid conditions were accompanied by brutal threats.
By the time the cardinals staggered out, two months later, one of their number had died, and the new Pope expired 16 days after his election.
Worse was to come.
The longest conclave in Church history resulted in a wait of two years and nine months before the election of a new pope.
It began in 1268 in the town of Viterbo, north of Rome, and it soon became apparent the cardinals were in no hurry to reach a decision.
After two years had elapsed, local people became so impatient that they tore off the roof of the palace where the cardinals were staying.
Bread and water
Whether it was to allow in the Holy Spirit or the rain is not clear, but the voters began to suffer.
Two cardinals died, and a third was forced to leave the conclave because he became so ill.
Eventually, in 1271, the new pontiff emerged, and took the name Gregory X.
Clearly scarred by the experience, he gave orders that in future the cardinals' rations should be gradually reduced once they were in conclave.
After five days, they would have to survive on bread and water. This would, he thought, concentrate their minds.
That rule was soon ignored, but by 1274 the system of closed conclaves had been established. It survives to this day, as one of the oldest forms of democratic election in the world.
Yet over the centuries, conclaves continued to drag on interminably, and the time spent by the cardinals pondering their choice did not guarantee that the right man would be chosen.
Better quarters
In 1294, the cardinals elected a hermit who became Celestine V. He quickly realised he was not up to the job and resigned.
What made the conclave experience worse was that they frequently took place in summer, when living conditions in closed buildings became intolerable.
In 1623, eight cardinals and forty of their assistants died of malaria.
But by keeping the electors shut off from the outside world, it did became harder for foreign powers to influence the election.
During the 20th Century, cardinals were given makeshift "cells" in the Apostolic Palace. They had to sleep on hard beds, and stumble around in the darkness, looking for bathrooms.
Having taken part in both the conclaves of 1978, John Paul II decided the cardinals deserved better quarters.
So they now have purpose-built accommodation, not unlike a modern hotel. It may not be the last word in luxury, but there are pleasant rooms with all mod cons.
But if the cardinals are too comfortable, maybe they will not be in such a rush to make up their minds.
Hopefully we will not have to starve them out.
