On 22 February 1495 Charles VIII and his chief commander, Louis II de La Trémoille, entered Naples almost without opposition. The speed and violence of the campaign left the Italians stunned. Realization struck them, especially the Venetians and the new Duke of Milan, Ludovico Sforza, that unless Charles was stopped Italy would soon just be another province of France. The Italian states rallied and on March 31 in Venice, the Holy League was proclaimed. The signatories were the Republic of Venice, the Duke of Milan, the Pope, the monarchs of Castile and Aragon, the King of England and the Holy Roman Emperor. The League engaged a veteran Condottiero, Francesco II of Gonzaga, Duke of Mantua to gather an army and expel the French from Italy. Upon hearing the news of the coalition assembled against him, Charles VIII left behing a garrisoning force in Naples and marched north with the remainder of his army, his artillery train and the considerable booty seized in the campaign thus far in order to join a smaller army under Louis II, Duke of Orléans in Piedmont in north-western Italy. While in Naples, the French army had been swept by an outbreak of syphilis and as the army moved north, it spread throughout Italy, where it became known as the "French Disease".