 Gaston VII added a third tower in the 13th century.Gaston Fébus (Gaston III of Foix and Gaston X of Béarn) added a brick donjon (keep), known as "la tour Billère" [the Tower of Billère].In 1464, Gaston IV of Foix-Béarn, after he married the Infanta Eleanor of Aragon, transferred his Court of Orthez to Pau.