Charlemagne was the eldest son of Pepin the Short and Bertrada of Laon, born before their canonical marriage. He became king of the Franks in 768 following his father's death, initially as co-ruler with his brother Carloman I, until the latter's death in 771. As sole ruler, 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. 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. Peter's Basilica in Rome.