Castile (; ) is a Spanish historical region of vague borders, which is the result of a gradual merge of the
Kingdom of Castile with its neighbours to become the
Crown of Castile and later the
Kingdom of Spain when united with the
Crown of Aragon and the
Kingdom of Navarre. In modern-day Spain, it is usually considered to comprise a part of the autonomous community of
Castile and León in the north-west, and
Castile–La Mancha and
Madrid in the center and the central-south-west of the country, sometimes including
Cantabria and
La Rioja in the north as well, for historical reasons. However, there are different versions about the exact boundaries of Castile, and since it lacks modern day official recognition, it has no official borders. It was traditionally divided between
Old Castile, which from 1833 was
Cantabria,
La Rioja and the eastern half of
Castile and León and
New Castile, which was
Castile–La Mancha and the
Community of Madrid. Modern Spanish monarchs are numbered according to the system of Castile.