Pope Leo XI, born Alessandro Ottaviano de' Medici, was Pope from 1 to 27 April 1605. His pontificate is one of the briefest in history having lasted under a month. He was from the prominent House of Medici originating from Florence.
On 14 March 1605, eleven days after the death of Clement VIII, 62 cardinals entered the conclave. Prominent among the candidates for the papacy were the great historian Cesare Baronius and the famous Jesuit controversialist Robert Bellarmine, future saint.
But Pietro Aldobrandini, the leader of the Italian party among the cardinals, allied with the French cardinals and brought about the election of Alessandro against the express wish of King Philip III of Spain. King Henry IV of France is said to have spent 300,000 écus in the promotion of Alessandro's candidacy.
On 1 April 1605, Cardinal Alessandro de' Medici was elected as pope. He chose to be called Leo XI in honor of his uncle Pope Leo X. He was crowned on 10 April 1605 by the protodeacon, Cardinal Francesco Sforza and he took possession of the Basilica of Saint John Lateran on 17 April 1605.
When he was elected, Leo XI was almost 70 years of age, and he died 27 days later. His death came as a result of fatigue and cold in the ceremony of taking possession of the Basilica of St John Lateran. He was called Papa Lampo ("Lightning Pope") because his papacy was so short.