 At the same time, the first Castilian viceroy, Diego Fernández de Córdoba, took an oath to respect Navarrese law, known as the "fueros".Initially the kingdom was attached to Ferdinand—and therefore to the Crown of Aragon—as an "earned good", falling back on the Papal bulls.Aragon was a Pyrenean realm with a similar confederate institutional make-up, as opposed to the authoritarian Castile.