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How did the long papal election after Clement IV’s death lead to the creation of the conclave system?

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Cardinals of the Catholic Church, dressed in red, sit at long tables in the Sistine Chapel during the 2005 papal election conclave, surrounded by ornate frescoed walls. — papal conclave Cardinals assembled inside the Sistine Chapel of the Vatican Palace for a conclave to elect a new pope; Vatican City, 2005.

The creation of the papal conclave system was a direct response to the extreme delays and turbulence that characterized papal elections in the 13th century. Following the death of Pope Clement IV in 1268, the cardinals failed to elect a successor for nearly three years.12

To force a resolution, the local magistrate in Viterbo took drastic measures: he locked the electors inside the episcopal palace, removed the roof to expose them to the elements, and restricted their diet to only bread and water until they finally selected Gregory X in 1271.1

Recognizing the necessity of preventing such prolonged vacancies and external interference, Gregory X promulgated a constitution at the Second Council of Lyon in 1274. This established the formal institution of the conclave—derived from the Latin cum clave, meaning "with a key"—which mandated that cardinals be sequestered in strict seclusion to conduct the election. This system, which cemented the College of Cardinals’ monopoly over the election, was later incorporated into canon law by Pope Boniface VIII.314