Charlemagne was the eldest son of Pepin the Short and Bertrada of Laon. He was born before their canonical marriage. He became king of the Franks in 768 following his fathers death, and was initially co-ruler with his brother Carloman I until the latters death in 771. As sole ruler, he continued his fathers policy towards protection of the papacy and became its sole defender, removing the Lombards from power in northern Italy and leading an incursion into Muslim Spain. He also campaigned against the Saxons to his east, Christianizing them (upon penalty of death) which led to events such as the Massacre of Verden. He 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. Peters Basilica in Rome.