Claim: Charlemagne reached the height of his strength in 800.

Charlemagne -LRB- -LSB- ˈʃɑːrlᵻmeɪn -RSB- -RRB- or Charles the Great -LRB- 2 April 742/747/74828 January 814 -RRB- , numbered Charles I , was the King of the Franks from 768 , King of the Lombards from 774 and Emperor of the Romans from 800 . He united much of Europe during the early Middle Ages . He was the first recognised emperor in western Europe since the fall of the Western Roman Empire three centuries earlier . The expanded Frankish state that Charlemagne founded was called the Carolingian Empire .   Charlemagne was the oldest son of Pepin the Short and Bertrada of Laon . He became king in 768 following his father 's death , initially as co-ruler with his brother Carloman I. Carloman 's sudden death in 771 in unexplained circumstances left Charlemagne as the undisputed ruler of the Frankish Kingdom . He continued his father 's policy towards the papacy and became its protector , removing the Lombards from power in northern Italy and leading an incursion into Muslim Spain . He campaigned against the Saxons to his east , Christianising them upon penalty of death and leading to events such as the Massacre of Verden . Charlemagne reached the height of his power in 800 when he was crowned Emperor of the Romans by Pope Leo III on Christmas Day at Old St. Peter 's Basilica .   Charlemagne has been called the `` Father of Europe '' -LRB- Pater Europae -RRB- , as he united most of Western Europe for the first time since the Roman Empire . His rule spurred the Carolingian Renaissance , a period of energetic cultural and intellectual activity within the Western Church . All Holy Roman Emperors considered their kingdoms to be descendants of Charlemagne 's empire , up to the last Emperor Francis II and the French and German monarchies .   However , the Eastern Orthodox Church views Charlemagne more controversially , labelling as heterodox his support of the filioque and recognition by the Bishop of Rome as legitimate Roman Emperor , rather than recognising Irene of Athens of the Eastern Roman Empire . These and other machinations led to the eventual split of Rome and Constantinople in the Great Schism of 1054 .   Charlemagne died in 814 , having ruled as emperor for thirteen years . He was laid to rest in his imperial capital of Aachen in what is today Germany . He married at least four times and had three legitimate sons , but only his son Louis the Pious survived to succeed him .