Karl der Große (Carolus Magnus, 'Charles the Great') became king of the Franks in 768 and over the next forty years built a realm spanning what is now France, Germany, the Low Countries, northern Italy, and parts of Spain. His reign was an effort to construct a new centre for a Western Europe that had remained politically fractured for centuries after Rome's collapse.

The staging of the Christmas Day coronation in St Peter's Basilica is still debated: did Pope Leo crown Charlemagne by surprise, or had the choreography been arranged in advance? Either way the symbolism was potent. The papacy was proclaiming a Western empire independent of the Byzantine emperor in Constantinople, who still styled himself 'Emperor of the Romans'. The move helped deepen the rift between Eastern and Western Christendom.

Charlemagne's reign sparked far more than military unification — it triggered the cultural revival known as the Carolingian Renaissance. A school was established at the palace at Aachen; ancient texts were recopied (a great many Latin classics we still read survive thanks to these scriptoria); and a new clear script, 'Carolingian minuscule', was developed to standardise the written word across the realm. Modern lowercase letterforms descend from it. His empire would be split among his grandsons after his death in 814 (Treaty of Verdun, 843) — but the idea of Europe and the seed of the Holy Roman Empire grew from this reign.