According to the chronicles of Alfonso III of Asturias; the first reference to the name "Castile" (Castilla) can be found in a document written during CE 800.

In Al-Andalus chronicles from the Cordoban Caliphate, the oldest sources refer to it as Al-Qila, or "the castled" high plains past the territory of Alava, more south to it and the first encountered in their expeditions from Zaragoza.

The name reflects its origin as a march on the eastern frontier of the Kingdom of Asturias, protected by castles, towers or castra.The County of Castile, bordered in the south by the Montes de Toledo,is repopulated by inhabitants of Cantabria, Asturias, Vasconia and Visigothic and Mozarab origins.

It has its own Romance dialect and customary laws.