This ruler's court was centered around a unique octagonal chapel at the royal capitol of Aachen, where this ruler died after bathing in the warm springs.
After a successful attack by the Saxons against this man, he retaliated by executing 4500 Saxons in a single day.  His focus on the destruction of Pamplona led to his inability to capture Zaragoza.  He put down a revolt by Hunald, and distaste with his wife Fastrada led to a minor revolt by Pepin the Hunchback.  This ruler's court was centered around a unique octagonal chapel at the royal capitol of Aachen, where this ruler died after bathing in the warm springs. The brother of Carloman and son of Pepin the Short, FTP, identify this second Carolingian king, crowned emperor of the Romans by Pope Leo III in 800, with a name meaning "Charles the Great."
After a successful attack by the Saxons against this man, he retaliated by executing 4500 Saxons in a single day.  
{Charlemagne} (Accept {Charles the Great} until mentioned; Accept {Charles Magnus} or {Carolus Magnus})