In early December, a Spanish force commanded by Ugo de Moncada landed near Genoa, intending to interfere in a conflict between pro-Valois and pro-Habsburg factions in the city. Francis dispatched a larger force under the Marquis of Saluzzo to intercept them. Confronted by the more numerous French and left without naval support by the arrival of a pro-Valois fleet commanded by Andrea Doria, the Spanish troops surrendered. Francis then signed a secret agreement with Pope Clement VII, who pledged not to assist Charles in exchange for Francis's assistance with the conquest of Naples. Against the advice of his senior commanders, Francis detached a portion of his forces under the Duke of Albany and sent them south to aid the Pope. Lannoy attempted to intercept the expedition near Fiorenzuola, but suffered heavy casualties and was forced to return to Lodi by the intervention of the infamous Black Bands of Giovanni de' Medici, Italian mercenaries which had just entered French service. Medici then returned to Pavia with a supply train of gunpowder and shot gathered by the Duke of Ferrara; but the French position was simultaneously weakened by the departure of nearly 5,000 Grisons Swiss mercenaries, who returned to their cantons in order to defend them against marauding landsknechts.