For this reason, both nations appointed commissioners to elucidate the exact water border in the conflicts of the towns of Fuenterrabía and Hendaye, something that until then had been solved by agreement.

To prevent another invasion, the fortification proceeded, ordering in November of that year the construction of a castle in Behovia, which reinforced the effectiveness of the Fuenterrabía fort.

At the beginning of October 1521 the castle of Behovia was taken by the troops commanded by the French Admiral Guillermo Goufier, Lord of Bonnivet, with hardly any casualties, since little resistance was offered.

He next surrounded the fortress of Fuenterrabía on October 6, taking it twelve days later, after three assaults by Navarrese and Gascon volunteers, among which nearly a thousand casualties occurred.

He received a significant increase in troops from different places, between 3000 and 4,000 German Landsknechts, and soldiers recruited in Castile, Navarre, Aragón, Vizcaya, La Rioja and Álava.

Later, different explosive charges were arranged to destroy its walls, but its fuses were extinguished by the Castilian troops under the command of Captain Ochoa Sanz de Asua, who took the castle.