The Colonna family suffered a major disaster, when Pompeo's uncle, Prospero Colonna, was defeated and captured at Battle of Marignano on 14 September 1515. Prospero had been the leading general of the Sforza of Milan, and had been leading a force of Milanese and Papal troops, along with the Swiss, against the Genoese, who were reinforced by the French, led by the young King Francis I and the Chevalier Bayard. Prospero was defeated, captured, and deported to France. Bishop Pompeo Colonna made the journey to France to effect his release. Travelling in the middle of the winter of 1515–1516, he was caught in an avalanche which engulfed an embassy from Sion just a few steps in front of him. Reaching France, he spent six months until the French king made a decision. King Francis, meditating on a plan to reclaim the Angevin kingdom of Naples, and realizing that he would need the friendly cooperation of the Pope and assistance in the Papal States, generously agreed to release Prospero Colonna, on the condition that Prospero agree in writing to serve under Francis' banner. Having reached Italy, however, Prospero began to raise troops to put at the disposal of Charles V at the siege of Verona. Prospero sent his nephew Pompeo on an embassy to the Emperor Maximilian and King Charles, and charged him with winning over King Ferdinand, Max's grandson. In this he was successful. Ferdinand provided Pompeo with money, and he proceeded through Germany to Bruxelles, where he engaged in discussions with Prince Charles, who was then Duke of Burgundy and an Austrian Archduke. He was then recalled to Rome by his uncle.