The Siege of Viana occurred from 1506 to 1507, when the army of King John III of Navarre besieged the castle of Viana, held by the rebellious noble Louis II de Beaumont, who was loyal to King Ferdinand II of Aragon.
King John III and Queen Catherine of Navarre welcomed John's brother-in-law Cesare Borgia to their court in Navarre, despite Borgia being branded as an outlaw in Spain and Italy. Borgia was given supreme command over the army of Navarre by King John, who intended to enlist Borgia's help in crushing a rebellion against his rule by lords supporting King Ferdinand, who sought to unite the Iberian Peninsula under Spanish rule. In March 1507, Borgia and 10,000 troops were sent to besiege Louis II de Beaumont's castle of Viana, and Borgia's cannon destroyed the town and the surrounding countryside. The Navarrese infantry were able to move into the town and fight the Spanish soldiers there, and cannons and siege towers attacked Viana Castle itself. The Navarrese soldiers attacked the city guards, tortured and killed civilians, and burnt down homes in the city, and several waves of soldiers reinforced the attack. Cesare Borgia made the mistake of pursuing some fleeing Spanish knights without realizing that he was by himself, and the knights succeeded in mortally wounding Borgia with a spear. He was stripped of all of his luxurious garments, valuables, and a leather mask covering half of his disfigured, syphilis-afflicted face. However, the Navarrese would succeed in capturing Viana, a minor victory against the Spanish-backed rebels. The victory was pyrrhic, however, as the death of Cesare Borgia sent shockwaves throughout southern and western Europe.