Pope Clement VII. Portrait by Sebastiano del Piombo, c. 1531.

The growing power of Holy Roman Emperor Charles V alarmed Pope Clement VII, who perceived Charles as attempting to dominate the Catholic Church and Italy. In an effort to free both from Imperial domination (i.e. from the Habsburg dynasty), Clement VII formed an alliance with Charles V’s arch-enemy, King Francis I of France, which came to be known as the League of Cognac.

The army of the Holy Roman Emperor defeated the French army in Italy, but funds were not available to pay the soldiers. The 34,000 Imperial troops mutinied and forced their commander, Charles III, Duke of Bourbon and Constable of France, to lead them towards Rome. Apart from some 6,000 Spaniards under the Duke, the army included some 14,000 Landsknechte under Georg von Frundsberg, some Italian infantry led by Fabrizio Maramaldo, the powerful Italian cardinal Pompeo Colonna and Luigi Gonzaga, and also some cavalry under command of Ferdinando Gonzaga and Philibert, Prince of Orange. Though Martin Luther himself was not in favor of attacking Rome or the Pope, some who considered themselves followers of Luther’s Protestant movement viewed the Papal capital as a target for religious reasons, and shared with the soldiers a desire for the sack and pillage of a city that appeared to be an easy target. Numerous bandits, along with the League's deserters, joined the army during its march.

The Duke left Arezzo on 20 April 1527, taking advantage of the chaos among the Venetians and their allies after a revolt broke out in Florence against Pope Clement VII’s family, the Medici. In this way, the largely undisciplined troops sacked Acquapendente and San Lorenzo alle Grotte, and occupied Viterbo and Ronciglione, reaching the walls of Rome on 5 May.

The sack of Rome in 1527, by Johannes Lingelbach, 17th century (private collection).

Holy Roman Imperial Army in 1527 When the Imperial Army in 1527 had defeated a French army in northern Italy, its commander found himself unable to pay his mercenaries, 34,000 of them mutinied and forced him to lead them towards Rome. Most of them were goaded by the possibility of rewarding plunder, but some of them might also, at least partly, have been religiously motivated. Several of the 14 000 German Landsknechte were Protestants. During its march through Italy, the rebelling army was joined by a motley crew of common bandits and various insurgents. The Roman defense was weak, a 5 000 men strong group of vigilantes and 186 Papal Swiss Guards, who at the last moment managed to bring the Pope to safety in Castel Sant'Angelo. Like a storm swell the undisciplined mercenaries inundated the city and indulged themselves in an orgy of ruthless violence. House after house was plundered, anyone who dared to offer resistance was killed immediately. Unarmed priests and monks were hardest hit, while nuns were dragged to brothels or sold in the streets to the murderous rabble. Churches were stripped of everything of value, tombs were broken up in a crazed the hunt for treasures. Saint Peter´s Basilica was used as stable, archives and libraries were torched after book pages had been torn out to be used as bedding for the horses. Lutheran Landsknechte chose a pope of their own, dressed themselves up in ecclesial robes and tottered brawling back and forth through the city streets. After having paid 400 000 ducats for his life, the disgraced Clement VII was given safe passage out of the city. After eight months of violence and madness the soldiery began to leave the devastated city. Food was running out, while thousands of rotting corpses lied unburied and all manner of vermin poisoned wells and groundwater, the plague spread among soldiers and the ransacked civilian population.

The imperial troops were 14,000 Germans, 6,000 Spanish, and an uncertain number of Italian infantry. The troops defending Rome were not at all numerous, consisting of 5,000 militiamen led by Renzo da Ceri and 189 Papal Swiss Guard. The city's fortifications included the massive walls, and it possessed a good artillery force, which the Imperial army lacked. Duke Charles needed to conquer the city swiftly, to avoid the risk of being trapped between the besieged city and the League's army.

On 6 May, the Imperial army attacked the walls at the Gianicolo and Vatican Hills. Duke Charles was fatally wounded in the assault, allegedly shot by Benvenuto Cellini. The Duke was wearing his famous white cloak to mark him out to his troops, but it also had the unintended consequence of pointing him out as the leader to his enemies. The death of the last respected command authority among the Imperial army caused any restraint in the soldiers to disappear, and they easily captured the walls of Rome the same day. Philibert of Châlon took command of the armies, but he was not as popular or feared, leaving him with little authority.

In the event known as the Stand of the Swiss Guard, the Swiss, alongside the garrison's remnant, made their last stand in the Teutonic Cemetery within the Vatican. Their captain, Kaspar Röist, was wounded and later sought refuge in his house, where he was killed by Spanish soldiers in front of his wife. The Swiss fought bitterly, but were immensely outnumbered and almost annihilated. Some survivors, accompanied by a band of refugees, fell back to the Basilica steps. Those who went toward the Basilica were massacred, and only 42 survived. This group of 42, under the command of Hercules Goldli, managed to stave off the Habsburg troops pursuing the Pope's entourage as it made its way across the Passetto di Borgo, which was a secret corridor that still connects the Vatican City to Castel Sant'Angelo.

After the brutal execution of some 1,000 defenders of the Papal capital and shrines, the pillage began. Churches and monasteries, as well as the palaces of prelates and cardinals, were looted and destroyed. Even pro-Imperial cardinals had to pay to save their properties from the rampaging soldiers. On 8 May, Cardinal Pompeo Colonna, a personal enemy of Clement VII, entered the city. He was followed by peasants from his fiefs, who had come to avenge the sacks they had suffered by Papal armies. However, Colonna was touched by the pitiful conditions of the city and hosted in his palace a number of Roman citizens.

The Vatican Library was saved because Philibert had set up his headquarters there. After three days of ravages, Philibert ordered the sack to cease, but few obeyed. In the meantime, Clement remained a prisoner in Castel Sant'Angelo. Francesco Maria della Rovere and Michele Antonio of Saluzzo arrived with troops on 1 June in Monterosi, north of the city. Their cautious behaviour prevented them from obtaining an easy victory against the now totally undisciplined Imperial troops. On 6 June, Clement VII surrendered, and agreed to pay a ransom of 400,000 ducati in exchange for his life; conditions included the cession of Parma, Piacenza, Civitavecchia and Modena to the Holy Roman Empire (however, only the last could be occupied in fact). At the same time Venice took advantage of this situation to capture Cervia and Ravenna, while Sigismondo Malatesta returned to Rimini.

Sack of Rome. 6 May 1527. By Martin van Heemskerck (1527).

Charles V with his hunting dog, oil on wood by Jakob Seisenegger, 1532;

Often cited as the end of the Italian High Renaissance, the Sack of Rome impacted the histories of Europe, Italy, and Catholicism, creating lasting ripple effects throughout world culture and politics.

Before the Sack, Pope Clement VII opposed the ambitions of Emperor Charles V and the Spanish, whom he correctly believed wished to dominate Italy and the Church. Afterward, he was no longer able to fight against them, lacking the military and financial resources to do so. To avert more warfare, the Pope adopted a conciliatory policy toward the Emperor. Charles V turned this to his political advantage, exerting increasing control over the Papacy and much of Italy.

The Sack had major repercussions for Italian society and culture, and in particular, for Rome. Pope Clement VII's War of the League of Cognac would be the last fight for Italian independence and unity until the nineteenth century. Rome, which had been a center of Italian High Renaissance culture and patronage before the Sack, suffered depopulation and economic collapse, causing artists and thinkers to scatter. The city's population dropped from some 55,000 before the attack to 10,000 afterward. An estimated 6,000 to 12,000 people were murdered. Many Imperial soldiers also died in the aftermath, largely from diseases caused by masses of unburied corpses in the streets. Pillaging finally ended in February 1528, eight months after the initial attack, when the city's food supply ran out, there was no one left to ransom, and plague appeared. Clement VII would continue artistic patronage and building projects in the city, but a perceived Medici golden age had passed. Rome, however, was largely rebuilt under later Popes, and its population reached 100,000 inhabitants during the century.

Landsknechte, etching by Daniel Hopfer, c. 1530 (W) (W) The Landsknechte (singular: Landsknecht, pronounced [ˈlantsknɛçt]) were largely German-speaking mercenaries, consisting predominantly of pikemen and supporting foot soldiers, who became an important military force in early modern Europe. Their front line was formed by doppelsöldner, renowned for their use of arquebus and zweihänder in the early modern period. They formed the bulk of the Imperial Army (Holy Roman Empire) from the late 1400s to the early 1600s.

A power shift — away from the Pope, toward the Emperor — likewise produced lasting consequences for Catholicism. The Emperor, for his part, was greatly embarrassed that his troops imprisoned the Pope; however, he'd sent armies to Italy with the goal of bringing the latter under his control. After doing so, Charles V set about reforming the Church in his own image. Clement VII, now making decisions under duress from the Emperor, rubber-stamped the latter’s demands — among them naming cardinals nominated by the latter, unworthy from any religious standpoint (although it is important to note that during the 1500s, many cardinals were appointed on the basis of familial connections); crowning Charles Holy Roman Emperor at Bologna in 1530; and refusing to annul the marriage of Charles' beloved aunt, Catherine of Aragon, to King Henry VIII of England, prompting the English Reformation. Likewise, without any conditions, Clement agreed to cede the worldly and political possessions of the bishopric of Utrecht to Charles' family, the Habsburgs. Cumulatively, these actions changed the complexion of the Church, steering it away from Renaissance freethought personified by Clement VII, toward the religious orthodoxy exemplified by the Counterreformation. After Clement's death in 1534, under the influence of Charles V and particularly his son King Phillip II of Spain (1556-1598), the Inquisition became pervasive, and the humanism encouraged by Renaissance culture came to be viewed as contrary to the teachings of the Church.

The Sack also contributed to making permanent the split between European Catholics and Protestants. Before the Sack, the Emperor and Pope disagreed over how to address Martin Luther and the Protestant Reformation, which was then growing in the Emperor's German territories.

Charles advocated for calling a Church Council. Clement opposed this based on historical precedent, believing that he would be deposed or killed — technically on account of his illegitimate birth but, in actuality, due to Charles' desire for a more pliable Pope. Clement advocated for fighting a Holy War to unite Christendom. Charles opposed this because his armies and treasury were then occupied in fighting other wars. After the Sack, the Pope relented to Charles' wishes, agreeing to call a Church Council and naming the city of Trent as its site. Clement VII did not convene the Council of Trent during his lifetime though, fearing the event, under Charles' aegis, would be a dangerous trap and powerplay. In 1545, eleven years after Clement's death, his successor Pope Paul III convened the Council of Trent, which as the Emperor predicted, did much to reform the corruption then present in certain orders of the Catholic Church. However, by 1545, the moment for reconciliation between Catholics and Protestants — arguably a possibility during the 1520s, given cooperation between the Pope and Emperor — had passed. In assessing the effects of the Sack of Rome, Martin Luther commented: "Christ reigns in such a way that the Emperor who persecutes Luther for the Pope is forced to destroy the Pope for Luther" (LW 49:169).

In commemoration of the Swiss Guard's bravery in defending Pope Clement VII during the Sack of Rome, recruits to the Swiss Guard are sworn in on 6 May every year.

Sack of Rome, by Francisco Javier Amérigo Aparicio, 1884. Biblioteca Museu Víctor Balaguer.