When did the Empire of Charles the Great flourish?

In 768, Charles came to power in Frankia. He spends conquest campaigns for a long period of time. Thus, during the years of his reign, the Frankish state was able to significantly expand its territories. So the empire included: the lands of Spain, Italy, France and Germany. The heyday of Charles’s empire falls in the years 800-814. However, after this there is a decline. In 843, the Treaty of Verdun was signed, which caused the split of the empire.