The French army was led by King Francis I of France, who laid siege to the city of Pavia (then part of the Duchy of Milan within the Holy Roman Empire) in October 1524 with 26,200 troops. The French infantry consisted of 6,000 French soldiers and 17,000 foreigners: 8,000 Swiss mercenaries and 9,000 German-Italian black bands. The French cavalry consisted of 2,000 "gendarmes" and 1,200 lances fournies. Charles V, intending to break the siege, sent a relief force of 22,300 troops under the command of the Fleming Charles de Lannoy, Imperial captain and viceroy of Naples, and of the French renegade Charles III, Duke of Bourbon. The Habsburg infantry consisted of 12,000 German Landsknechte, 5,000 Spaniards, and 3,000 Italians, and its command was exercised by an Italian Condottiero, the Marquis of Pescara, in conjunction with the German military leader Georg Frundsberg and the Spanish captain Antonio de Leyva who was in charge of an Imperial garrison inside Pavia. The cavalry, led by Lannoy and Bourbon, consisted of 1,500 knights and 800 lances.