The foundation of the Holy Roman Empire is usually dated to the decision of Charlemagne (742-814), king of the Franks, to assume an imperial title on Christmas Day, 800. The exact reasons for this remain a matter of dispute, but were clearly related to Charlemagne’s personal mission to establish Christian rule in western and central Europe. The original empire was partitioned in 843, with the eastern portion retaining the association with the Christian imperial mission. This assumed greater ideological significance with the coronation of Otto I (r. 936-973) in Rome in 962 as he consciously invoked not only continuity with Charlemagne’s empire, but that of ancient Rome. The concept of "imperial translation" claimed that the empire was a direct continuation of that of ancient Rome in its final, Christian configuration, and so was the last of the four "world monarchies" prophesied in the Bible to rule over the earth before the Day ofJudgment. Such ideas buttressed the emperor’s claim to be the supreme overlord of all other Christian rulers and thus the secular arm of a single, universal Christendom, leading to a prolonged dispute with the papacy.
The Christianizing mission combined with internal population growth to push the empire across the river Elbe early in the twelfth century, making it the largest polity in Europe until the growth of the Russian Empire in the eighteenth century. This expansion was assisted by the relative continuity of three successive imperial dynasties: the Ottonians (919-1024), the Salians (1024-1125), and the Staufers (1138-1254). However, the growth of more distinct kingdoms in western Europe restricted the emperor’s practical authority to the lands east of the Rhine and north of the Alps. Moreover, the emperor only ruled a small portion of the vast area directly, relying on a host of secular and spiritual lords, as well as autonomous cities to manage local and regional affairs. These lords (increasingly called "princes") and cities evolved as the "imperial estates" (Reichsstande) between the thirteenth and sixteenth centuries, each controlling a distinct territory within the empire, with their own subordinate clergy, nobility, towns, and rural communes.
The absence of a single imperial dynasty after 1254 assisted this process and led to an elective imperial title that became entrenched in Germany and could be assumed without papal participation. Following the demise of the Luxembourg dynasty (1347-1437), the title passed by election to the Habsburgs, who retained it with only a single break (1740-1745) until the end of the empire in 1806. The onset of prolonged warfare with France and the Ottomans coincided with the confessional strife of the Reformation, and social and economic change. These pressures forced constitutional change from the late fifteenth century, creating an elaborate web of written and customary rights intended to preserve the autonomy of the imperial estates and the corporate structure of central European society within a hierarchical political framework under the emperor’s overall authority, but not his direct rule. The growth of Austria and Prussia as distinct European great powers undermined this structure from within and led to its collapse during the Napoleonic Wars when the last emperor abdicated in 1806.
