Its Christian roots can be traced back to the early 10th century when a monastery for Saint John the Baptist was erected on the grounds.

Isidore was archbishop of Seville, and the most celebrated academic and theologian of Visigothic Spain in the period preceding the Arab invasions.

With the agreement of Abbad II al-Mu'tadid, the Muslim ruler of Seville, Isidore's relics were brought to Leon where they could be interred on Christian soil.

It was the first sample of modern parliamentarism in the history of Europe, according to the UNESCO and John Keane's book The Life and Death of Democracy.

Sancha's brother, Bermudo III, declared the war against Castile and Castilian troops, with the help of Navarre, killed the Leonese king, becoming Ferdinand I of León.

Today eleven kings, numerous queens and many nobles lie interred beneath the polychrome vaults of the medieval "royal pantheon".

The 12th century painted murals are in an exceptional state of preservation and consist of an ensemble of New Testament subjects along with scenes of contemporary rural life.

The library holds 300 medieval works, numerous manuscripts as well as mozarabic bible dating from 960 and a Latin version transcribed in the seventh century.