Complex sentence: After the Siege of Pavia in 774, Charlemagne allowed Hrodgaud to keep the duchy, which was continued under the Franks until 828, when it was divided into counties and broken up.
Split into simpler sentences: After the Siege of Pavia in 774, Charlemagne allowed Hrodgaud to keep the duchy. The duchy continued under Frankish rule until 828, when it was divided into counties and broken up.