Aragon, an ancient kingdom of Spain. It lay on the French border, midway from the Bay of Biscay to the Mediterranean. Saragossa on the Ebro was the capital. Aragon grew from 1035 to 1497 to be one of the two important kingdoms of Spain. Castile was the other. In the last named year the two kingdoms were united by the marriage of their sovereigns, Ferdinand of Aragon and Isabella of Castile.