The Colonna had meanwhile organized an attack on Rome, defeating the Papal forces and briefly seizing control of the city in March 1526; they had soon been soon paid off and departed, however.

The Imperial army has defeated the French army in Italy, but funds are not available to pay the soldiers.

The thirty-four thousand Imperial troops mutiny and force their commander, Charles III of Bourbon, to lead them towards Rome.

Apart from some six thousand Spaniards under the Duke, the army includes some fourteen thousand Landsknechts 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 is not in favor of it, some who consider themselves followers of Luther's Protestant movement view the Papal capital as a target for religious reasons, and share with the soldiers a desire for the sack and pillage of a very rich city that appear to be an easy target.

Numerous bandits, along with the League's deserters, join the army during its march.

The Duke leaves Arezzo on April 20, 1527, taking advantage of the chaos among the Venetians and their allies after a revolt that has broken out in Florence against the Medici.

In this way, …

…San Lorenzo alle Grotte, and …

…occupy Viterbo and …

…Ronciglione, …

…reaching the walls of Rome on May 5.

The troops defending Rome are not at all numerous, consisting of five thousand militiamen led by Renzo da Ceri and one hundred and eighty-six Papal Swiss Guard.

The city's fortifications include the massive walls, and it possessed a good artillery force, which the Imperial army lacks.

Duke Charles needs to conquer the city hastily, to avoid the risk of being trapped between the besieged city and the League's army.

The Imperial army attacks the walls at the Gianicolo and Vatican Hills on May 6.

Duke Charles is fatally wounded in the assault, allegedly shot by Benvenuto Cellini.

The Duke is wearing his famous white cloak to mark him out to his troops, but it also has 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 causes any restraint in the soldiers to disappear, and they easily capture the walls of Rome the same day.

Philibert of Châlon takes command of the armies, but he is not as popular or feared, leaving him with little authority.

One of the Swiss Guard's most notable hours occurs at this time.

Almost the entire guard is massacred by Imperial troops on the steps of St Peter's Basilica.

Of the one hundred and eighty-nine guards on duty only the forty-two who accompany the pope survive, but the bravery of the rearguard ensures that Pope Clement VII escapes to safety, down the Passetto di Borgo, a secret corridor that still links the Vatican City to Castel Sant'Angelo.

The pillage begins after the brutal execution of some one thousand defenders of the Papal capital and shrines.

Churches and monasteries, as well as the palaces of prelates and cardinals, are looted and destroyed.

Even pro-Imperial cardinals have to pay to save their properties from the rampaging soldiers.

Cardinal Pompeo Colonna, a personal enemy of Clement VII, enters the city on May 8, followed by peasants from his fiefs, who have come to avenge the sacks they had suffered by Papal armies.

Colonna is touched, however, by the pitiful conditions of the city and hosts a number of Roman citizens in his palace.

The Vatican Library is saved because Philibert had set up his headquarters there.

After three days of ravages, Philibert orders the sack to cease, but few obey.

In the meantime, Clement remains a prisoner in Castel Sant'Angelo.

Francesco Maria della Rovere and Michele Antonio of Saluzzo arrive with troops on June 1 in Monterosi, north of the city.

Their cautious behavior prevents them from obtaining an easy victory against the now totally undisciplined Imperial troops.

On June 6, Clement VII surrenders, and agrees to pay a ransom of four hundred thousand ducati in exchange for his life; conditions include the cession of Parma, Piacenza, Civitavecchia and Modena to the Holy Roman Empire (however, only the last can be occupied in fact).

At the same time, …

…Venice takes advantage of his situation to capture Cervia and …

…Ravenna, while …