The most powerful of the Carolingian rulers was Charlemagne, who fought more than fifty campaigns and became the greatest warrior of the early Middle Ages. Through brutal military expeditions that brought wealth — lands, booty, slaves, and tribute — and by peaceful travel, personal appearances, shrewd marital alliances, and the sheer force of his personality, Charlemagne sought to awe newly conquered peoples and rebellious domestic enemies. By around 805 the Frankish kingdom included all of continental Europe except Spain, Scandinavia, southern Italy, and the Slavic fringes of the East.

For administrative purposes, Charlemagne divided his entire kingdom into counties. Each of the approximately six hundred counties was governed by a count, who had full military and judicial power and held his office for life but could be removed by the emperor for misconduct. As a link between local authorities and the central government, Charlemagne appointed officials called missi dominici, “agents of the lord king.” Each year beginning in 802 two missi, usually a count and a bishop or abbot, visited assigned districts. They checked up on the counts and their districts’ judicial, financial, and clerical activities.

In the autumn of the year 800 Charlemagne visited Rome, where on Christmas Day Pope Leo III crowned him emperor. The event had momentous consequences. In taking as his motto Renovatio romani imperi (Revival of the Roman Empire), Charlemagne was deliberately perpetuating old Roman imperial ideas while identifying with the new Rome of the Christian Church. From Baghdad, the Abbasid Empire’s caliph, Harun al-Rashid (r. 786–809), congratulated Charlemagne on his coronation with the gift of an elephant. The elephant survived for nearly a decade, though like everyone else at Charlemagne’s capital of Aachen (on the western border of modern Germany), it lived in a city that was far less sophisticated, healthy, and beautiful than Abbasid Baghdad. Although the Muslim caliph recognized Charlemagne as a fellow sovereign, the Byzantines regarded his papal coronation as rebellious and Charlemagne as a usurper. His crowning as emperor thus marked a decisive break between Rome and Constantinople and gave church authorities in the West proof that the imperial title could only be granted by the pope.

As he built an empire through conquest and strategic alliances, Charlemagne also set in motion a cultural revival that later historians called the “Carolingian Renaissance.” The Carolingian Renaissance was a rebirth of interest in, study of, and preservation of the language, ideas, and achievements of classical Greece and Rome. Scholars at Aachen copied Greco-Roman and Christian books and manuscripts and created libraries housed in churches and monasteries. Furthermore, Charlemagne urged monasteries to promote Christian learning, and both men’s and women’s houses produced beautiful illustrated texts, preserving Christian and classical works for subsequent generations.

Charlemagne left his vast empire to his sole surviving son, Louis the Pious (r. 814–840), who attempted to keep the empire intact. This proved to be impossible. Members of the nobility engaged in plots and open warfare against the emperor, often allying themselves with one of Louis’s three sons. In 843, shortly after Louis’s death, those sons agreed to the Treaty of Verdun, which divided the empire into three parts: Charles the Bald received the western part, Lothair the middle and the title of emperor, and Louis the eastern part, from which he acquired the title “the German.” Though of course no one knew it at the time, this treaty set the pattern for political boundaries in Europe that have been maintained through today. Other than brief periods under Napoleon and Hitler, Europe would never again see as large a unified state as it had under Charlemagne, which is one reason he has become a symbol of European unity in the twenty-first century.

The weakening of central power was hastened by invasions and migrations from the north, south, and east. Thus Charlemagne’s empire ended in much the same way that the Roman Empire had earlier, from a combination of internal weakness and external pressure.