The Portuguese kingdom, a former southern county split from the Kingdom of Galicia and fief of the Kingdom of Leon, was created by Afonso I of Portugal in 1126 and expanded towards the Islamic south, like its neighbouring kingdoms. That part of Galicia, named Portugal, became independent while the northern part of the country remained under the Kingdom of León during the 12th century and early 13th century. Northern Galicia would later be ruled by the Kingdom of Castile, which would become the core and ethnic base for the future Spain; but the culture was the same on both sides of the political border. Galician-Portuguese culture attained great prestige during the Low Middle Ages. In the late 15th century, Castilian domination became harder, banishing their language in all official uses, including the church.