throughout June 1520. The following month, Henry sought an agreement with Charles at Gravelines. Charles was crowned King of the Romans at Aachen in October 1520, but not Holy Roman Emperor, which could only happen if he was crowned by the pope in Rome. To divert Charles—and his army—from entering and possibly taking control of Italy, Francis sought to wage war on the emperor by proxy, and made plans for simultaneous incursions into German and Spanish territory. Luxembourg was attacked under the leadership of Robert de la Marck, whilst a French-Navarrese army simultaneously advanced through Navarre after reconquering St-Jean-Pied-de-Port. The expedition was nominally led by the 18-year-old Navarrese king Henry d'Albret, whose kingdom had been invaded by Ferdinand II of Aragon in 1512, but the army was effectively commanded by André de Foix and funded and equipped by the French. The French plans proved to be flawed, as the intervention of Henry of Nassau drove back the Luxembourg offensive; and although de Foix was initially successful in seizing Pamplona, he was driven from Navarre after being defeated at the Battle of Esquiroz on 30 June 1521. Charles was meanwhile preoccupied with the issue of Luther, whom he confronted at the Diet of Worms in April 1521. Pope Leo X was unwilling to tolerate open defiance of his own authority, and considered the Emperor as a potential ally to support him against Luther, whose backers included Frederick of Saxony. In May 1521, Charles proclaimed the Edict of Worms against Luther, whilst also aiding the Pope in the return of Parma and Piacenza to Italian authority. Leo, needing the Imperial mandate for his campaign against what he viewed as a dangerous heresy, promised to assist in expelling the French from Lombardy, leaving Francis with only the Republic of Venice for an ally. Initial moves (June 1521 – May 1522) On 20 August 1521, the Imperial army under Henry of Nassau invaded northeastern France—an attack made in response to de Marck’s attack on Luxembourg. Ardres was overrun, Mouzon was severely damaged after being besieged, and Aubenton was sacked and its inhabitants massacred. The attackers were delayed during the three-week siege of Mézières by the resistance of the French, led by Pierre Terrail, seigneur de Bayard. Francis had time to raise a large army at Reims for relieving Mézières. The town was resupplied a few days before the king's army arrived at the town