on 26 September, which was by then largely destroyed. Nassau was forced to withdraw, laying waste to towns along his route of his retreat. Tournai, which had been returned to France by Henry VIII in February 1519 as part of the terms of the Treaty of London, was besieged by Imperial forces. Tournai was left to surrender to the besiegers after Francis's army was ordered to retreat, and later disbanded. A Franco-Navarrese force approached the fortress of Amaiur (Baztan, Navarre), laying siege to the fortress the Castilians had just reinforced. On 3October 1521 the Castilians capitulated in exchange for free passage to Castile. The troops of Guillaume Gouffier then headed to Labourd and on to Behobia, capturing the fortress of Urantzu. Fuenterrabia, at the mouth of the river Bidasoa on the Franco-Spanish border, was captured later in the month by French-Navarrese troops under Bonnivet and Claude of Lorraine. The French held this advantageous foothold in northern Spain until March 1524. On 28 November 1521 Charles V and Henry VIII signed in secret the Treaty of Bruges. Odet de Foix, Vicomte de Lautrec, the French governor of Milan, was tasked with resisting the Imperial and Papal forces. Lautrec was outmatched by Prospero Colonna, and by late November 1521 had been forced out of Milan and had retreated to located towns around the river Adda. Lautrec's army was reinforced by Swiss mercenaries. Unable to pay them, he had to give in to their demands to engage the Imperial forces immediately. On 27 April 1522, Lautrec attacked Colonna's combined Imperial and Papal army near Milan at the Battle of Bicocca. Lautrec had planned to use his superiority in artillery to his advantage, but the Swiss, impatient to engage the enemy, masked his guns and charged against the entrenched Spanish arquebusiers. In the resulting melee, the Swiss were badly mauled by the Spanish and by a force of landsknechts (Germanic mercenaries). Their morale broken, the Swiss returned to their cantons; Lombardy was abandoned. Colonna and d'Avalos, left unopposed, proceeded to besiege Genoa, capturing the city on 30 May. France at bay The loss of Lombardy was followed by England entering openly into the conflict, when on 29 May 1522, the English formally declared war on France. Henry VIII and Charles signed the Treaty of Windsor on 16 June 1522. The treaty outlined a joint English-Imperial attack against France. Charles agreed to compensate England for