(Deliberations started in 1268, when Catholic cardinals met in the village of Viterbo to elect a new Pope.
Monsignor Charles Burns, a retired archivist at the Secret Vatican Archives, told ABC News in 2005 that the villagers grew angry at how long the process was taking (there was a split between French and Italian factions), and locked the cardinals in a nearby palace (the term "conclave" actually refers to this — it means "with a key").
In the end, the process went on for so long that the villagers tried to starve the cardinals into making a decision, giving them only bread and water. They even tore the roof off the palace in a bid to expose the cardinals to the elements — you can still see the roof-less palace today:
They chose Italian born Teobaldo Visconti, a man who was neither a cardinal nor even a priest Gregory, an Italian born as was away fighting the crusades. It took him 8 months to return, whereupon he became Gregory X. But it means there was no pope for 3 years, and the world did not end.)