Pope Pius III

He was born Francesco Todeschini Piccolomini in Siena. As the nephew of Pius II by his sister Laodamia, he was received into favour by that pontiff, who permitted him to assume the name and arms of the Piccolomini family, and raised him, when only twenty-two years of age, to the see of Siena and the cardinalate. He was employed by subsequent popes in several important legations, as by Paul II at the diet of Ratisbon, and by Sixtus IV to secure the restoration of ecclesiastical authority in Umbria.

Amid the disturbances consequent upon the death of Alexander VI he was, by the not wholly disinterested influence of Cardinal Rovera, elected pope on September 22, 1503, his installation taking place on the October 8 following. He at once took in hand the reform of the papal court and arrested Caesar Borgia; but after a brief pontificate of twenty-six days he died (October 18, 1503) of an ulcer in the leg, or, as some have alleged, of poison administered at the instigation of Pandolfo Petrucci, governor of Siena.

See Pope John Paul I for another example of a short pontificate generating conspiracy theories.