Carolingian emperor (817/840–855) whose wars against his brothers ended in the Treaty of Verdun, which partitioned Charlemagne's empire and shaped the map of Europe.
Lothair I was Carolingian emperor from 840 to 855, the eldest son of Louis the Pious and grandson of Charlemagne. Made co-emperor and heir to the whole empire by his father in 817, he spent his life fighting to preserve that inheritance intact against his father and his brothers, who each sought a share of the vast realm.
The struggle culminated after Louis the Pious's death in a civil war among the brothers, in which Lothair was defeated at the great Battle of Fontenoy in 841. The Treaty of Verdun in 843 then partitioned the empire: Lothair kept the imperial title and a long central strip — the "Middle Kingdom" running from the North Sea through Lotharingia to Italy — while his brothers took the eastern and western Frankish lands that would become Germany and France.
Lothair was born in 795, the eldest son of Louis the Pious and grandson of Charlemagne. In 817 his father issued the Ordinatio Imperii, making Lothair co-emperor and principal heir, with his younger brothers to hold subordinate kingdoms — an attempt to keep the empire united under one supreme ruler. Lothair was also given the kingdom of Italy.
But Louis the Pious's later attempts to provide for a son by his second marriage, Charles the Bald, upset this settlement and set the family at war.
Lothair I is remembered as an able but rigid and often overbearing prince, fiercely attached to the principle of imperial unity — and to his own supremacy within it. As the designated heir to the whole empire, he defended that inheritance with determination and no little ruthlessness, repeatedly rebelling against his own father when the succession was altered, and warring on his brothers to hold the empire together under his crown.
That attachment to unity was both his cause and his limitation: he could not accept the partition of Charlemagne's legacy, yet he lacked the power to prevent it, and his defeats forced him to the very division he had fought to avoid. In his later years he grew weary of the struggle, and his final act — abdicating to die a monk after dividing his own realm among his sons — has an air of resignation. He appears as the last serious champion of a united Carolingian empire, defeated by the centrifugal forces of his house.
On Louis the Pious's death in 840, Lothair claimed authority over the whole empire as emperor, but his brothers Louis the German and Charles the Bald resisted. In 841 the two younger brothers combined and crushed Lothair at the bloody Battle of Fontenoy; the following year they sealed their alliance with the famous Oaths of Strasbourg.
Unable to impose his will, Lothair came to terms. By the Treaty of Verdun in 843, the empire was divided into three: Charles the Bald received the western lands (the kernel of France), Louis the German the eastern (the kernel of Germany), and Lothair kept the imperial title together with a long, awkward central kingdom stretching from Frisia and Lotharingia down through Burgundy to Italy.
Worn out by decades of conflict, Lothair abdicated in 855, dividing his Middle Kingdom among his three sons — Italy and the imperial title to Louis II, Lotharingia to Lothair II, and Provence to Charles — and retired to the monastery of Prüm, where he died within days, on 29 September 855.
Lothair I is remembered as the emperor whose wars and defeat brought about the Treaty of Verdun, the partition that shattered Charlemagne's empire and drew the first outlines of France and Germany. His own Middle Kingdom, a fragile band with no natural unity, soon fragmented — and the disputed lands of Lotharingia that bore his name would be fought over between its western and eastern neighbours for a thousand years. His reign marks the beginning of the political division of Western Europe.