Complex sentence: Written after 787, it is a continuation of his previous major historical work, the "Historia Romana", which was based on the "Breviarium" of Eutropius, with six books added describing historical events up to Justinian's empire.
Split into simpler sentences: Written after 787, it is a continuation of his previous major historical work, the "Historia Romana". This was an adjustment of Eutropius' "Breviarium" with six books added describing the events up to Justinian's empire.