The 1559 papal conclave (5 September – 25 December) was convened on the death of Pope Paul IV and elected Pope Pius IV as his successor. Due to interference from secular rulers and the cardinals' disregard for their supposed isolation from the outside world, it was the longest conclave of the 16th century.

Death and preparations Pope Paul IV died on 18 August 1559, aged 83. His church reforms had mainly been based on repressive measures such as the Inquisition and the Index of Forbidden Books – he had no confidence in the Council of Trent, dissolving it in 1552 and not reviving it.

Even cardinals were accused of heresy – at the time of Paul IV's death, Cardinal Morone was a prisoner of the Inquisition in the castel Sant' Angelo. Paul IV, fearing that Morone might become his successor, issued the papal bull Cum ex officio Apostolatus, which stipulated that a heretic could not be validly elected pope – however, this was in vain since the College of Cardinals released Morone after Paul's death and allowed him to take part in the conclave. The bull also covered Cardinal d'Este, who Paul complained was trying to become pope by simony.

Paul IV's reforms did not abolish nepotism, however – 3 of the cardinals at the conclave were Paul's nephews, the most influential being Carlo Carafa and the other two being Diomede Carafa and Alfonso Carafa. On the model of pope Alexander VI (one of the Borgia popes, who had died on the same date as Paul 56 years earlier), Paul had tried to build up his family's power in Italy, mainly at the expense of the Colonna family, whose many lands (including the imperial Palia fiefdom) were seized and handed over to the Carafa family. Paul's nephews ruled even more brutally than he and abused their power so much that at one point Paul was forced to step in, stripping Carlo of power early in 1559. Carlo never regained his uncle's favour and after Paul's death he and Paul's other two cardinal-nephews had good reason to fear their enemies would now take revenge.

Paul IV was rigidly orthodox, intolerant, and authoritarian in manner. Spontaneous riots broke out in Rome after his death, with crowds toppling his statue and attacking the Inquisition's headquarters. Thus 3700 troops were brought in to keep order, including 300 cavalry.

Cardinals in 1559

Participants At the time of the conclave there were 55 cardinals, 47 of whom participated in it. Of those 47, one died during the conclave (Capodiferro) and two had to leave early due to illness:Miranda, Salvador. "Conclave of September 5 to December 25, 1559", The Cardinals of the Holy Roman Church

Jean du Bellay (made a cardinal on 21 May 1535) – cardinal-bishop of Ostia e Velletri; dean of the College of Cardinals; administrator of the archdiocese of Bordeaux (left the conclave on 13 December due to illness ) François de Tournon (9 March 1530) – cardinal-bishop of Sabina; sub-dean of the College of cardinals; archbishop of Lyon and primate of Gaul; general of the order of canons regular Rodolfo Pio di Carpi (22 December 1536) – cardinal-bishop of Porto e Santa Rufina; administrator of the diocese of Girgenti Francesco Pisani (1 July 1517) – cardinal-bishop of Frascati; cardinal priest of San Marco; administrator of the archdiocese of Narbonne Federico Cesi (19 December 1544) – cardinal-bishop of Palestrina; administrator of the diocese of Cremona Pedro Pacheco de Villena (16 December 1545) – cardinal-bishop of Albano; bishop of Sigüenza Robert de Lenoncourt (20 December 1538) – cardinal-priest of S. Cecilia; protopriest of the College of Cardinals; archbishop of Embrun; administrator of the diocese of Auxerre Ercole Gonzaga (3 May 1527) – cardinal-priest of S. Maria Nuova; bishop of Mantua; protector of the Spanish Niccolò Caetani (22 December 1536) – cardinal-priest of S. Eustachio; archbishop of Capua; administrator of the diocese of Quimper Giovanni Girolamo Morone (2 June 1542) – cardinal-priest of S. Maria in Trastevere; bishop of Novara; protector of the Austrians Cristoforo Madruzzo (2 June 1542) – cardinal-priest of S. Cesareo in Palatio; bishop of Trent and Brixen Bartolomé de la Cueva (19 December 1544) – cardinal-priest of S. Croce in Gerusalemme Georges d'Armagnac (19 December 1544) – cardinal-priest of S. Lorenzo in Lucina; bishop of Rodez Otto Truchess von Waldburg (19 December 1544) – cardinal-priest of S. Sabina; bishop of Augsburg; protector of the Holy Roman Empire Tiberio Crispi (19 December 1544) – cardinal-priest of S. Agata alla Suburra; administrator of the archdiocese of Amalfi; camerlengo of the College of Cardinals Giovanni Angelo Medici (8 April 1549) – cardinal-priest of S. Prisca Cristoforo Ciocchi del Monte (20 November 1551) – cardinal-priest of S. Prassede; bishop of Cagli Fulvio della Corgna, O.S.Io.Hieros. (20 November 1551) – cardinal-priest of S. Stefano al Monte Celio Giovanni Michele Saraceni (20 November 1551) – cardinal-priest of S. Anastasia; archbishop of Acerenza and Matera (19 December left the conclave due to illness) Giovanni Ricci (20 November 1551) – cardinal-priest of S. Vitale, Gervasio e Protasio Giovanni Andrea Mercurio (20 November 1551) – cardinal-priest of S. Ciriaco alla Terme; archbishop of Messina Giacomo Puteo (20 November 1551) – cardinal-priest of S. Maria in Via; archbishop of Bari; protector of the Johannites Giovanni Battista Cicala (20 November 1551) – cardinal-priest of S. Clemente; administrator of the diocese of Mariana Gianbernardino Scotti, Theat. (20 December 1555) – cardinal-priest of S. Matteo in Merulana; archbishop of Trani Diomede Carafa (20 December 1555) – cardinal-priest of S. Martino ai Monti; bishop of Ariano Scipione Rebiba (20 December 1555) – cardinal-priest of S. Pudenziana; archbishop of Pisa Jean Suau (20 December 1555) – cardinal-priest of S. Giovanni a Porta Latina; bishop of Mirepoix Giovanni Antonio Capizzuchi (20 December 1555) – cardinal-priest of S. Pancrazio; bishop of Lodi Taddeo Gaddi (15 March 1557) – cardinal-priest of S. Silvestro in Capite; archbishop of Cosenza Lorenzo Strozzi (15 March 1557) – cardinal-priest of S. Balbina; bishop of Béziers Jean de Bertrand (15 March 1557) – cardinal-priest of SS. Nereo ed Achilleo; administrator of the archdiocese of Sens Antonio Michele Ghislieri, O.P. (15 March 1557) – cardinal-priest of S. Maria sopra Minerva; Grand Inquisitor of the Holy Congregation of the Roman and Universal Inquisition; bishop of Sutri and Nepi Clemente d'Olera, O.F.M.Obs. (15 March 1557) – cardinal-priest of S. Maria in Aracoeli; archpriest of Rapallo Alessandro Farnese (18 December 1534) – cardinal-deacon of S. Lorenzo in Damaso; protodeacon of the College of Cardinals; Vice-Chancellor of the Holy Roman Church; legate in Avignon; archpriest of the Lateran Basilica; administrator of the diocese of Spoleto; protector of the Poles Guido Ascanio Sforza (18 December 1534) – cardinal-deacon of S. Maria in Via Lata; camerlengo of the Holy Roman Church; archpriest of the Lateran Basilica; administrator of the diocese of Parma; protector of the Portuguese Ippolito II d'Este (20 December 1538) – cardinal-deacon of S. Maria in Aquiro; administrator of the archdiocese of Auch; gubernator of Tivoli; protector of the French Giacomo Savelli (19 December 1539) – cardinal-deacon of S. Maria in Cosmedin; administrator of the diocese of Nicastro Girolamo Capodiferro (19 December 1544) – cardinal-deacon of S. Giorgio in Velabro; bishop of Saint-Jean-de-Maurienne (died 1 December) Ranuccio Farnese (16 December 1545) – cardinal-deacon of S. Angela in Pescheria; Grand Penitentiary; archpriest of the Lateran Basilica; administrator of the archdiocese of Ravenna Giulio Feltre della Rovere (27 July 1547) – cardinal-deacon of S. Pietro in Vincoli Innocenzo del Monte (30 May 1550) – cardinal-deacon of S. Onofrio Luigi Cornaro (20 November 1551) – cardinal-deacon of S. Teodoro Louis I de Guise (22 December 1553) – cardinal-deacon of S. Tommaso in Parione; administrator of the diocese of Albi Girolamo Simoncelli (22 December 1553) – cardinal-deacon of SS. Cosma e Damiano; bishop of Orvieto Carlo Carafa (7 June 1555) – cardinal-deacon of SS. Vito e Modesto; regent of the Apostolic Chancellery; administrator of the diocese of Comminges; gubernator of Ancona, Rimini i Gualdo Alfonso Carafa (15 March 1557) – cardinal-deacon of S. Maria in Domnica; librarian of the Holy Roman Church; regent of the Apostolic Chamber; administrator of the archdiocese of Naples Vitellozzo Vitelli (15 March 1557) – cardinal-deacon of S. Maria in Portico; bishop of Città di Castello

Of these 47 cardinals, 37 were Italians, 7 French, 2 Spanish and 1 German. 13 had been appointed by Pope Paul IV, 11 by Pope Julius III, 20 Pope Paul III, 2 by Pope Clement VII and 1 by Pope Leo X.

Absentees 8 cardinals (5 French, 1 Spanish, 1 Portuguese and 1 Italian) did not come to the conclave. 2 of these 8 died during its sitting:

Claude de Longwy de Givry (7 November 1533, by Clement VII) – Cardinal-Priest of Sant'Agnese in Agone, administrator of the diocese of Langres Odet de Coligny de Châtillon (7 November 1533, by Clement VII) – Cardinal-Deacon of Sant' Adriano, administrator of the diocese of Beauvais Sanguin Antoine de Meudon (19 December 1539, by Pope Paul III) – Cardinal-Priest of San Crisogono, administrator of the Archdiocese of Toulouse (died 25 November) Francisco Mendoza de Bobadilla (19 December 1544, by Paul III) – Cardinal-Priest of San Eusebio, bishop of Burgos Henry of Portugal (16 December 1545, by Paul III) – Cardinal-Priest of Santi Quattro Coronati, Archbishop of Evora, inquisitor general of the Portuguese Inquisition, papal legate in Portugal Charles I of Lorraine-Guise (27 July 1547, by Paul III) – Cardinal-Priest of Sant' Apollinare, Archbishop of Reims Charles II de Bourbon-Vendôme (8 January 1548, by Paul III) – Cardinal-Deacon of Santo Sisto, Archbishop of Rouen Girolamo Dandini (20 November 1551, by Julius III) – Cardinal-Priest of Santo Marcello (died 4 December)

Factions and candidates The College of Cardinals was divided into three factions: a Spanish one (17 Cardinals headed by cardinals Sforza and Madruzzo), a French one (16 cardinals headed by Ippolito d'Este and de Guise) and an "Italian" one (14 cardinals headed by Carlo Carafa and Alessandro Farnese). A few cardinals remained neutral.Setton, Kenneth Meyer. The Papacy and the Levant, 1204-1571, American Philosophical Society, 1984 The Spanish ambassador, Don Francisco de Vargas Mejía, regularly slipped into the conclave to counsel the Spanish group.

The French candidates for pope were d'Este, Gonzaga and Tournon. The King of France favoured Cardinal Carpi. Philip II of Spain preferred cardinals Carpi, Morone, Puteo, Medici and D'Oler – in short, any candidate other than d'Este or a Frenchman. Cosimo I, Duke of Florence, favored, although no relation, Cardinal Giovanni Angelo de' Medici, younger brother of Gian Giacomo Medici, an Imperial general in Germany and Siena. In total there were over 20 candidates.

For Carlo Carafa, choosing the new pope was literally a matter of life and death and so he mainly used the conclave to obtain guarantees that he and his relatives would not be punished for their abuses. He had one serious advantage – the Italian cardinals nominated by his uncle Paul remained loyal to him. He favoured Carpi and Gonzaga for pope. Although his uncle was an enemy of the Spanish, and encouraged France, Carlo decided to ally himself with the Spanish party.

Course The papacy was under criticism for failing to address abuses, and the college of cardinals was split between moderates and conservatives, as well as along national lines.