Complex sentence: He chose the Frank Rampó, who had already faithfully served Charlemagne, and who had been charged to communicate the death of the Emperor to his son Louis I, then king of Aquitania, in Doue (Anjou) at the beginning of 814.
Split into simpler sentences: He chose the Frank Rampó, who had already faithfully served Charlemagne. He had been charged to communicate the death of the Emperor to his son Louis, then king of Aquitaine, in Doue, Anjou, at the beginning of 814.