When the Carolingian Empire fragmented during the ninth century, its strongest surviving core was the East Frankish kingdom — a loose confederation of German-speaking duchies. Otto I of the Saxon dynasty (936–973) decisively halted Magyar raids at the Battle of Lechfeld (955) and emerged as the clear power centre of central Europe. Meanwhile in Italy, Pope John XII was under pressure from Berengar II and needed protection. At the pope's invitation, Otto crossed the Alps.

The ceremony at St Peter's Basilica on 2 February 962 was a conscious replay of Charlemagne's coronation of 800. Otto presented himself as direct heir to the Carolingians and therefore to Rome. The 'Privilegium Ottonianum', issued the same year, set out the division of authority between pope and emperor on paper: the pope crowns the emperor, the emperor protects the pope. In practice the balance was fragile — Otto soon had the same pope deposed.

The founding fixed two fault lines in medieval Europe. First, the contest between papacy and empire over the right to invest bishops (the Investiture Controversy) would explode in the eleventh and twelfth centuries, reaching Canossa and the Concordat of Worms (1122). Second, the idea of 'Rome' had now been uncoupled from the geographic city, becoming an abstract label of legitimacy attached to German lands — what Voltaire would much later mock as neither holy, nor Roman, nor an empire.

And yet the structure endured. Under the name 'Sacrum Imperium Romanum' it survived into the nineteenth century, until Napoleon dissolved it in 1806. This long-lived shell shaped the political frame of German-speaking Europe, the rise of Austria and the Habsburgs, the confessional map of the Reformation, and the polycentric tradition that preceded modern Germany.