Complex sentence: This area was conquested by Ostrogoths, Lombards and Byzantines, prior Charlemagne defeat the last Lombard king and subsequently the city became part of the Germanic Holy Roman Empire as a semi-republic.
Split into simpler sentences: This area was conquered by Ostrogoths, Lombards and Byzantines, prior Charlemagne's defeat the last Lombard king. Subsequently the city became part of the Germanic Holy Roman Empire as a semi-republic.