Viana Castle was a large fortified stronghold in Viana, Kingdom of Navarre, which was conquered by Spain in 1512. In 1507, the castle was held by Louis de Beaumont at the time that it was besieged by Cesare Borgia and King John's army of 10,000 men.
Siege of Viana
Following his escape from Valencia, Cesare Borgia allied himself with his cousin-in-law, John III of Navarre. John III tasked Cesare to besiege Viana and its fortification in 1507, due to his military expertise. However, the Assassin Mentor Ezio Auditore da Firenze was tracking Cesare during this period, and eventually located him in Viana.
Ezio fought his way through the castle's exterior fortifications, where he encountered Cesare, who managed to escape. The Assassin then managed to mount Viana Castle's walls by climbing a siege tower, where he found Cesare on one of the castle's battlements, leading to a duel between the pair. On Cesare's defeat and subsequent demise, John III's troops eventually abandoned their attempt to reclaim the castle.