Complex sentence: The Frankish kings of the Merovingian dynasty retained a good deal of the Roman system of administration, including the title "comes" which preserved its original meaning: a companion of the king, a royal servant of high rank.
Split into simpler sentences: The Frankish kings of the Merovingian dynasty retained a good deal of the Roman system of administration. This included the role and title of "comes", which preserved its original meaning: a companion of the king, a royal servant of high rank.