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Why did Louis I make Lothar I coemperor?
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Louis I
Louis the Pious as a Christian Roman Emperor, portrait from De laudibus sanctae crucis by Rabanus Maurus.
Louis I made his eldest son, Lothar I, coemperor in 817 through the issuance of the Ordinatio imperii.12
Louis I designed this decree to address the challenges of maintaining the unity of the empire while simultaneously providing for his sons. By establishing Lothar as coemperor, Louis intended to ensure the empire remained a cohesive entity after his death, while assigning his younger sons, Pippin and Louis the German, to subordinate roles as kings of Aquitaine and Bavaria, respectively. Under this arrangement, the younger brothers were to remain under the general suzerainty of Lothar, thereby preserving the central authority of the imperial office.21