The Frankish king crowned Emperor of the Romans on Christmas Day 800 CE who unified most of Western Europe under a single ruler for the first time since the Roman Empire's fall, promoted literacy and learning in the Carolingian Renaissance, and whose empire — despite fragmenting within a generation of his death — became the template for European political and religious identity that persisted for a thousand years.
On Christmas Day, 800 CE, Pope Leo III set a crown on Charlemagne’s head and hailed him Emperor of the Romans — a title Charlemagne neither sought nor saw coming, at least according to his own biographer. In that instant a pope revived an empire three centuries dead and claimed the right to make emperors, a claim that would set church against crown for the next thousand years.