The sack of Rome in 1527 was an unintended consequence of the ongoing rivalry between Emperor Charles V, of the Habsburg dynasty, and the French king Francis I, of the Valois line. Francis and Charles had been at war over contested territories in Spain, Burgundy, and Italy. In 1525, the French army was defeated in Pavia and Francis taken as a prisoner in Madrid until he signed the 1526 Treaty of Madrid. The agreement forced Francis to turn over numerous Valois lands, including Burgundy, and marry Charles’ sister. Upon returning to France, however, he reneged on the pact and resumed war against the imperial forces. While Adrian VI had sided with Charles, his papal successor Clement VII feared the increasing power of the emperor and so joined the League of Cognac with France, Venice, Florence, and Milan. Charles responded by conscripting his generals to northern Italy to lead the imperial troops against the defensive front.
The imperial army, largely composed of Germans and Swiss, had long gone without wages and resisted direction. Instead, they laid siege to Rome in May 1527. The city had been rebuilt with Renaissance splendor over the preceding century and the sack laid it to waste. Clement VII fled for his safety to castle Sant’ Angelo, later to Orvieto, where he would remain until the fall of 1528. The pope was in effect imprisoned by Charles. The war between the emperor and Francis continued until the Peace of Cambrai in 1529. Burgundy was restored to Francis and the rivalry between the two families set aside so they could address a common threat, the Turkish army, as well as deal with the ongoing tensions over Luther’s reformation. In the process, Rome was made subject to Charles and the pope would ultimately confirm him as emperor by crowning him in Bologna in 1530. Luther famously said of the episode, “Christ reigns in such a way that the emperor who persecuted Luther for the pope is forced to destroy the pope for Luther” (LW 49:169).