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Memory and historiography

Charlemagne was a frequent subject of, and inspiration for, medieval writers after his death. Einhard's Vita Karoli Magni, according to Johannes Fired, "can be said to have revived the defunct literary genre of the secular biography." Einhard drew on classical sources, such as Suetonius' The Twelve Caesars, the orations of Cicero, and Tacitus ' Agricola to frame his work's structure and style. The Carolingian period also saw a revival of the mirrors for princes genre. The author of the Latin poem Visio Karoli Magni, written c. 865, uses facts (apparently from Einhard) and his own observations on the decline of Charlemagne's family after their civil wars later in the ninth century as the bases of a visionary tale about Charles meeting a prophetic spectre in a dream. Notker 's Gesta Karoli Magni, written for Charlemagne's great-grandson Charles the Fat, presents moral anecdotes (exempla) to highlight the emperor's qualities as a ruler.

Charlemagne, as a figure of myth and emulation, grew over the centuries; Matthias Becher writes that over 1,000 legends are recorded about him, far outstripping subsequent emperors and kings. Later medieval writers depicted Charlemagne as a crusader and Christian warrior. Charlemagne is the main figure of the medieval literary cycle known as the Matter of France. Works in this cycle, which originated during the Crusades, centre on characterizations of the emperor as a leader of Christian knights in wars against Muslims. The cycle includes chansons de geste (epic poems) such as the Song of Roland and chronicles such as the Historia Caroli Magni, also known as the (Pseudo-)Turpin Chronicle. Charlemagne was depicted as one of the Nine Worthies, a fixture in medieval literature and art as an exemplar of a Christian king. Despite his central role in these legends, author Thomas Bulfinch noted that "romancers represent him as often weak and passionate, the victim of treacherous counsellors, and at the mercy of turbulent barons, on whose prowess he depends for the maintenance of his throne."

Attention to Charlemagne became more scholarly in the early modern period as Eindhard's Vita and other sources began to be published. Political philosophers debated his legacy; Montesquieu viewed him as the first constitutional monarch and protector of freemen, but Voltaire saw him as a despotic ruler and representative of the medieval period as a Dark Age. As early as the sixteenth century, debate between German and French writers began about Charlemagne's "nationality". These contrasting portraits—a French Charlemagne versus a German Karl der Große —became especially pronounced during the nineteenth century with Napoleon's use of Charlemagne's legacy and the rise of German nationalism. German historiography and popular perception focused on the Massacre of Verden, emphasized with Charlemagne as the "butcher" of the Germanic Saxons or downplayed as an unfortunate part of the legacy of a great German ruler. Propaganda in Nazi Germany initially portrayed Charlemagne as an enemy of Germany, a French ruler who worked to take away the freedom and native religion of the German people. This quickly shifted as Adolf Hitler endorsed a portrait of Charlemagne as a great unifier of disparate German tribes into a common nation, allowing Hitler to co-opt Charlemagne's legacy as an ideological model for his expansionist policies.

Historiography after World War II focused on Charlemagne as "the father of Europe" rather than a nationalistic figure, a view first advanced during the nineteenth century by German romantic philosopher Friedrich Schlegel. This view has led to Charlemagne's adoption as a political symbol of European integration. Modern historians increasingly place Charlemagne in the context of the wider Mediterranean world, following the work of Henri Pirenne.