In the 5C, Millán de Berceo and a few disciples withdrew here to live a hermitic life. Upon the death of Millán in 574, his tomb became a destination for pilgrims. In the 10C, a monastery and Mozarab church (Suso) were built, and in 1053 monks settled in the valley (Yuso). The first manuscripts in the Castilian language were written here. The two monasteries became a designated UNESCO World Heritage Site in 1997.