The Old Spanish Kingdom was a medieval kingdom that existed in the Iberian Peninsula from the 8th century until the 15th century. It was composed of four main kingdoms: Castile, Aragon, Leon, and Asturias. Castile was the largest and most powerful of the four kingdoms, and it was located in the central part of the peninsula. Aragon was located in the northeast, Leon in the northwest, and Asturias in the northwest. All four kingdoms were united under one ruler in the late 15th century, forming the Kingdom of Spain.