The Sack of Rome, then part of the Papal States, followed the capture of the city on 6 May 1527 by the mutinous troops of Charles V, Holy Roman Emperor during the War of the League of Cognac. Rioting over unpaid salaries, the German Landsknechte, many of whom were Protestant, together with Spanish soldiers and Italian mercenaries, entered the city of Rome and immediately began looting, slaying and holding citizens for ransom. The sack debilitated the League of Cognac, an alliance formed by France, Milan, Venice, Florence and the Papacy against Charles V. Pope Clement VII took refuge in Castel Sant'Angelo after the Swiss Guard were annihilated in a delaying rearguard action, where he remained until a ransom was paid to the pillagers. By February 1528 lack of food and an outbreak of plague led to the armies abandoning the city, whose population had dropped from 55,000 to 10,000. Benvenuto Cellini, eyewitness to the events, described the sack in his works.