|Native name||Congiura dei Pazzi|
|Date||26 April 1478, Easter Sunday|
|Location||Duomo of Florence|
|Also known as||Pazzi plot|
|Non-fatal injuries||Lorenzo de' Medici, wounded|
In the aftermath of the plot many of the conspirators – and others accused of being conspirators – were executed, some by hanging from the windows of the Palazzo della Signoria; there were some eighty executions in all. The surviving Pazzi family members were banished from Florence.
Francesco della Rovere, who came from a poor family in Liguria, was elected pope in 1471. As Sixtus IV, he was both wealthy and powerful and at once set about giving power and wealth to his nephews of the della Rovere and Riario families. Within months of his election, he had made Giuliano della Rovere (the future pope Julius II) and Pietro Riario both cardinals and bishops; four other nephews were also made cardinals.: 252 : 128 He made Giovanni della Rovere, who was not a priest, prefect of Rome, and arranged for him to marry into the da Montefeltro family, dukes of Urbino.
For Girolamo Riario, also a layman – and who may in fact have been his son rather than his nephew – he arranged to buy Imola, a small town in Romagna, with the aim of establishing a new papal state in that area.: 252 : 128 Imola lay on the trade route between Florence and Venice. Lorenzo de' Medici had arranged in May 1473 to buy it from Galeazzo Maria Sforza, the duke of Milan, for 100,000 fiorini d'oro, but Sforza subsequently agreed to sell it instead to Sixtus for 40,000 ducats, provided that his illegitimate daughter Caterina Sforza was married to Riario.: 253 This purchase was to have been financed by the Medici bank, but Lorenzo refused, causing a rift with Sixtus and the termination of the appointment of the Medici as bankers to the Camera Apostolica.: 158 The pope negotiated with other bankers, and a substantial part of the cost was obtained from the Pazzi bank.
A further source of friction between Lorenzo and Sixtus was the status of the archbishopric of Florence, left vacant by the death of Pietro Riario in 1474. Lorenzo managed to obtain the appointment of his brother-in-law, Rinaldo Orsini, to the post. Among the possible candidates for the position was Francesco Salviati, a relative of the Pazzi family and friend of Francesco de' Pazzi, who later in 1474 was appointed archbishop of Pisa. The appointment was contested by the Florentines on the grounds that they had not given their assent.
Girolamo Riario, Francesco Salviati and Francesco de' Pazzi put together a plan to assassinate Lorenzo and Giuliano de' Medici. Pope Sixtus was approached for his support. He made a very carefully worded statement in which he said that in the terms of his holy office he was unable to sanction killing. He made it clear that it would be of great benefit to the papacy to have the Medici removed from their position of power in Florence, and that he would deal kindly with anyone who did this. He instructed the men to do what they deemed necessary to achieve this aim, and said that he would give them whatever support he could.: 254 An encrypted letter in the archives of the Ubaldini family, discovered and decoded in 2004, shows that Federico da Montefeltro was deeply embroiled in the conspiracy and had committed to position 600 troops outside Florence, waiting for the right moment.
The attack took place on the morning of Sunday, 26 April 1478, during High Mass at the Duomo of Florence. Unusually, Lorenzo and Giuliano were both present, and were attacked at the same time. Lorenzo was attacked by two of Jacopo Pazzi's men, but managed to escape to the sacristy, and thence to his home. Giuliano was killed by Bernardo Bandini dei Baroncelli and Francesco de' Pazzi. Francesco Salviati, with a number of Jacopo Pazzi's men, went to the Palazzo della Signoria and attempted to take control of it, but was unsuccessful – the Florentines did not rise against the Medici as the Pazzi had hoped they would. He was captured and, with Francesco de' Pazzi and several others, was hanged from the windows of the Palazzo della Signoria.: 140 
Many of the conspirators, as well as many people accused of being conspirators, were killed; more than thirty died on the day of the attack. Most were soon caught and summarily executed. Renato de' Pazzi was lynched and hanged. Jacopo de' Pazzi, head of the family, escaped from Florence but was caught and brought back. He was tortured, then hanged from the Palazzo della Signoria next to the decomposing corpse of Salviati. He was buried at Santa Croce, but the body was dug up and thrown into a ditch. It was then dragged through the streets and propped up at the door of Palazzo Pazzi, where the rotting head was mockingly used as a door-knocker. From there it was thrown into the Arno; children fished it out and hung it from a willow tree, flogged it, and then threw it back into the river.: 141
Lorenzo did manage to save the nephew of Sixtus IV, Cardinal Raffaele Riario, who was almost certainly an innocent pawn of the conspirators, as well as two relatives of the conspirators. The main conspirators were hunted down throughout Italy. Between 26 April, the day of the attack, and 20 October 1478, a total of eighty people were executed.: 456 Bandini dei Baroncelli, who had escaped to Constantinople, was arrested and returned in fetters by the Sultan Mehmed II, and – still in Turkish clothing – was hanged from a window of the Palazzo del Capitano del Popolo on 29 December 1479.: 142  There were three further executions on 6 June 1481.: 456
The Pazzi were banished from Florence, and their lands and property confiscated. Their name and their coat of arms were perpetually suppressed: the name was erased from public registers, and all buildings and streets carrying it were renamed; their shield with its dolphins was everywhere obliterated. Anyone named Pazzi had to take a new name; anyone married to a Pazzi was barred from public office.: 142 Guglielmo de' Pazzi, husband of Lorenzo's sister Bianca, was placed under house arrest,: 141 and later forbidden to enter the city; he went to live at Torre a Decima, near Pontassieve.
Sixtus IV reacted strongly to the death of Salviati: with a bull of 1 June 1478 he excommunicated Lorenzo, his supporters and all members of the current and preceding administration of the city. On 20 June he placed Florence under interdict, forbidding Mass and communion. By July troops of the Kingdom of Naples under the command of Alfonso of Aragon, and others from Urbino under Federico da Montefeltro, had begun to make attacks on Florentine territory. Lorenzo took an unorthodox course of action: he sailed to Naples and put himself in the hands of the king, Ferdinand I, who interceded on his behalf with the pope, though without success.: 189 
The events of the Pazzi conspiracy affected the developments of the Medici regime in two ways: they convinced the supporters of the Medici that a greater concentration of political power was desirable and they strengthened the hand of Lorenzo de' Medici, who had demonstrated his ability in conducting the foreign affairs of the city. Emboldened, the Medicean party carried out new reforms.: 223
Shortly after the attack Poliziano – who was in the Duomo when it took place – wrote his Pactianae coniurationis commentarium, a dramatic account of the conspiracy. It was published by Niccolò di Lorenzo della Magna; a revised edition appeared in 1480.: 157
- Vincent Cronin (1992 ). The Florentine Renaissance. London: Pimlico. ISBN 0712698744.
- Christopher Hibbert (1979 ). The Rise and Fall of the House of Medici. Harmondsworth, Middlesex: Penguin. ISBN 0140050906.
- Ingeborg Walter (2009). Medici, Lorenzo dei (in Italian). Dizionario Biografico degli Italiani, volume 73. Roma: Istituto dell'Enciclopedia Italiana. Accessed June 2021.
- Marta Celati (2020). Angelo Poliziano's Coniurationis commentarium: The Conspiracy Narrative as 'Official' Historiography. In: Marta Celati (2020). Conspiracy Literature in Early Renaissance Italy: Historiography and Princely Ideology. Oxford: Oxford University Press. ISBN 9780191895999. doi:10.1093/oso/9780198863625.001.0001/oso-9780198863625-chapter-5. (subscription required).
- Marcello Simonetta, The Montefeltro Conspiracy: A Renaissance Mystery Decoded, Doubleday (2008) ISBN 0385524684
- Nicholas Scott Baker (2009). For Reasons of State: Political Executions, Republicanism, and the Medici in Florence, 1480–1560. Renaissance Quarterly 62 (2): 444–478. doi:10.1086/599867. (subscription required).
- Guido Pampaloni (1963). Bandini dei Baroncelli, Bernardo (in Italian). Dizionario Biografico degli Italiani, volume 5. Roma: Istituto dell'Enciclopedia Italiana. Accessed August 2017.
- Vanna Arrighi (2015). Pazzi, Cosimo de' (in Italian). Dizionario Biografico degli Italiani, volume 82. Rome: Istituto dell'Enciclopedia Italiana. Accessed April 2018.
- Gino Benzoni (1995). Federico da Montefeltro, duca di Urbino (in Italian). Dizionario Biografico degli Italiani, volume 45. Rome: Istituto dell'Enciclopedia Italiana. Accessed April 2018.
- Lauro Martines (2003). April Blood: Florence and the Plot Against the Medici. Oxford: Oxford University Press. ISBN 9780195176094.
- Tobias Daniels (2013). La congiura dei Pazzi: i documenti del conflitto fra Lorenzo de' Medici e Sisto IV. Le bolle di scomunica, la "Florentina Synodus", e la "Dissentio" insorta tra la Santità del Papa e i Fiorentini. Florence: Edifir. ISBN 9788879706490.
- Nicolai Rubinstein (1997) The government of Florence under the Medici (1434–1494). Oxford: Oxford University Press.
- Emilio Bigi (1960). Ambrogini, Angelo, detto il Poliziano (in Italian). Dizionario Biografico degli Italiani, volume 2. Rome: Istituto dell'Enciclopedia Italiana. Accessed April 2018.