According to Sampiro, Fernando ("Fredenandi Ansuri filius") was one of the counts of the region of Burgos, the chief city of Castile—the others being Nuño Fernández, Abolmondar Albo, and Diego Rodríguez—who were captured by Ordoño II on the river Carrión in the place called Tebulare or Tegulare ("Tejar" or "Tejares" in Spanish, as yet unidentified) and imprisoned them in León.
It was built on the site of previous Roman baths of the 2nd century which, 800 years later, king Ordoño II converted into a palace.