During his reign in Aquitaine Louis was charged with the defence of the Empire's southwestern frontier. He reconquered Barcelona from the Muslims in 801 and re-asserted Frankish authority over Pamplona and the Basques south of the Pyrenees in 813. As emperor he included his adult sons—Lothair, Pepin, and Louis—in the government and sought to establish a suitable division of the realm between them. The first decade of his reign was characterised by several tragedies and embarrassments, notably the brutal treatment of his nephew Bernard of Italy, for which Louis atoned in a public act of self-debasement. In the 830s his empire was torn by civil war between his sons, only exacerbated by Louis's attempts to include his son Charles by his second wife in the succession plans. Though his reign ended on a high note, with order largely restored to his empire, it was followed by three years of civil war. Louis is generally compared unfavourably to his father, though the problems he faced were of a distinctly different sort.
Louis was crowned king of Aquitaine as a child in 781 and sent there with regents and a court. Charlemagne constituted the sub-kingdom in order to secure the border of his kingdom after his devastating defeat at the hands of Basques in Roncesvalles in (778).
In 794, Charlemagne settled four former Gallo-Roman villas on Louis, in the thought that he would take in each in turn as winter residence: Doué-la-Fontaine in today's Anjou, Ebreuil in Allier, Angeac-Charente, and the disputed Cassinogilum. Charlemagne's intention was to see all his sons brought up as natives of their given territories, wearing the national costume of the region and ruling by the local customs. Thus were the children sent to their respective realms at so young an age. Each kingdom had its importance in keeping some frontier, Louis's was the Spanish March. In 797, Barcelona, the greatest city of the Marca, fell to the Franks when Zeid, its governor, rebelled against Córdoba and, failing, handed it to them. The Umayyad authority recaptured it in 799. However, Louis marched the entire army of his kingdom, including Gascons with their duke Sancho I of Gascony, Provençals under Leibulf, and Goths under Bera, over the Pyrenees and besieged it for two years, wintering there from 800 to 801, when it capitulated. The sons were not given independence from central authority, however, and Charlemagne ingrained in them the concepts of empire and unity by sending them on military expeditions far from their home bases. Louis campaigned in the Italian Mezzogiorno against the Beneventans at least once.
Louis was one of Charlemagne's three legitimate sons to survive infancy, and, according to Frankish custom, Louis had expected to share his inheritance with his brothers, Charles the Younger, King of Neustria, and Pepin, King of Italy. In the Divisio Regnorum of 806, Charlemagne had slated Charles the Younger as his successor as emperor and chief king, ruling over the Frankish heartland of Neustria and Austrasia, while giving Pepin the Iron Crown of Lombardy, which Charlemagne possessed by conquest. To Louis's kingdom of Aquitaine, he added Septimania, Provence, and part of Burgundy.
But in the event, Charlemagne's other legitimate sons died — Pepin in 810 and Charles in 811 — and Louis alone remained to be crowned co-emperor with Charlemagne in 813. On his father's death in 814, he inherited the entire Frankish kingdom and all its possessions (with the sole exception of Italy, which remained within Louis's empire, but under the direct rule of Bernard, Pepin's son).
He was in his villa of Doué-la-Fontaine, Anjou, when he received news of his father's passing. Hurrying to Aachen, he crowned himself and was proclaimed by the nobles with shouts of Vivat Imperator Ludovicus.
In his first coinage type, minted from the start of his reign, he imitated his father Charlemagne's portrait coinage, giving an image of imperial power and prestige in an echo of Roman glory . He quickly enacted a "moral purge", in which he sent all of his unmarried sisters to nunneries, forgoing their diplomatic use as hostage brides in favour of the security of avoiding the entanglements that powerful brothers-in-law might bring. He spared his illegitimate half-brothers and tonsured his father's cousins, Adalard and Wala, shutting them up in Noirmoutier and Corbie, respectively, despite the latter's initial loyalty.
His chief councillors were Bernard, margrave of Septimania, and Ebbo, whom, born a serf, Louis would raise to the archbishopric of Rheims but who would ungratefully betray him later. He retained some of his father's ministers, such as Elisachar, abbot of St Maximin near Trier, and Hildebold, Archbishop of Cologne. Later he replaced Elisachar with Hildwin, abbot of many monasteries.
He also used Benedict of Aniane (the Second Benedict), a Septimanian Visigoth and monastic founder, to help him reform the Frankish church. One of Benedict's primary reforms was to ensure that all religious houses in Louis' realm adhered to the Rule of St Benedict, named for its creator, the First Benedict, Benedict of Nursia (480–550).
In 816, Pope Stephen V, who had succeeded Leo III, visited Rheims and again crowned Louis. The Emperor thereby strengthened the papacy by recognising the importance of the pope in imperial coronations.
If one of the subordinate kings died, he was to be succeeded by his sons. If he died childless, Lothar would inherit his kingdom. In the event of Lothar dying without sons, one of Louis the Pious' younger sons would be chosen to replace him by "the people". Above all, the Empire would not be divided: the Emperor would rule supreme over the subordinate kings, whose obedience to him was mandatory.
With this settlement, Louis tried to combine his sense for the Empire's unity, supported by the clergy, while at the same time providing positions for all of his sons. Instead of treating his sons equally in status and land, he elevated his first-born son Lothair above his younger brothers and gave him the largest part of the Empire as his share.
In 822, as a deeply religious man, Louis performed penance for causing Bernard's death, at his palace of Attigny near Vouziers in the Ardennes, before Pope Paschal I, and a council of ecclesiastics and nobles of the realm that had been convened for the reconciliation of Louis with his three younger half-brothers, Hugo whom he soon made abbot of St-Quentin, Drogo whom he soon made Bishop of Metz, and Theodoric. This act of contrition, partly in emulation of Theodosius I, had the effect of greatly reducing his prestige as a Frankish ruler, for he also recited a list of minor offences about which no secular ruler of the time would have taken any notice. He also made the egregious error of releasing Wala and Adalard from their monastic confinements, placing the former in a position of power in the court of Lothair and the latter in a position in his own house.
A greater Slavic menace was gathering on the southeast. There, Ljudevit Posavski, duke of Pannonia, was harassing the border at the Drava and Sava rivers. The margrave of Friuli, Cadolah, was sent out against him, but he died on campaign and, in 820, his margarvate was invaded by Slovenes. In 821, an alliance was made with Borna, duke of the Dalmatia, and Ljudevit was brought to heel. In 824 several Slav tribes in the north-western parts of Bulgaria acknowledged Louis's suzerainity and after he was reluctant to settle the matter peacefully with the Bulgarian ruler Omurtag, in 827 the Bulgarians attacked the Franks in Pannonia and regained their lands.
On the far southern edge of his great realm, Louis had to control the Lombard princes of Benevento whom Charlemagne had never subjugated. He extracted promises from Princes Grimoald IV and Sico, but to no effect.
On the southwestern frontier, problems commenced early when, in 815, Séguin, duke of Gascony, revolted. He was defeated and replaced by Lupus III, who was dispossessed in 818 by the emperor. In 820 an assembly at Quierzy-sur-Oise decided to send an expedition against the Cordoban caliphate. The counts in charge of the army, Hugh, count of Tours, and Matfrid, count of Orléans, were slow in acting and the expedition came to naught.
The birth of this son damaged the Partition of Aachen, as Louis's attempts to provide for his fourth son met with stiff resistance from his older sons, and the last two decades of his reign were marked by civil war.
At Worms in 829, Louis gave Charles Alemannia with the title of king or duke (historians differ on this), thus enraging his son and co-emperor Lothair, whose promised share was thereby diminished. An insurrection was soon at hand. With the urging of the vengeful Wala and the cooperation of his brothers, Lothair accused Judith of having committed adultery with Bernard of Septimania, even suggesting Bernard to be the true father of Charles. Ebbo and Hildwin abandoned the emperor at that point, Bernard having risen to greater heights than either of them. Agobard, Archbishop of Lyon, and Jesse, bishop of Amiens, too, opposed the redivision of the empire and lent their episcopal prestige to the rebels.
In 830, at Wala's insistence that Bernard of Septimania was plotting against him, Pepin of Aquitaine led an army of Gascons, with the support of the Neustrian magnates, all the way to Paris. At Verberie, Louis the German joined him. At that time, the emperor returned from another campaign in Brittany to find his empire at war with itself. He marched as far as Compiègne, an ancient royal town, before being surrounded by Pepin's forces and captured. Judith was incarcerated at Poitiers and Bernard fled to Barcelona.
Then Lothair finally set out with a large Lombard army, but Louis had promised his sons Louis the German and Pepin of Aquitaine greater shares of the inheritance, prompting them to shift loyalties in favour of their father. When Lothair tried to call a general council of the realm in Nijmegen, in the heart of Austrasia, the Austrasians and Rhinelanders came with a following of armed retainers, and the disloyal sons were forced to free their father and bow at his feet (831). Lothair was pardoned, but disgraced and banished to Italy. Pepin returned to Aquitaine and Judith - after being forced to humiliate herself with a solemn oath of innocence - to Louis's court. Only Wala was severely dealt with, making his way to a secluded monastery on the shores of Lake Geneva. Though Hilduin, abbot of Saint Denis, was exiled to Paderborn and Elisachar and Matfrid were deprived of their honours north of the Alps; they did not lose their freedom.
Soon Lothair, with the support of Pope Gregory IV, whom he had confirmed in office without his father's support, joined the revolt in 833. While Louis was at Worms gathering a new force, Lothair marched north. Louis marched south. The armies met on the plains of the Rothfeld. There, Gregory met the emperor and may have tried to sow dissension amongst his ranks. Soon much of Louis's army had evaporated before his eyes, and he ordered his few remaining followers to go, because "it would be a pity if any man lost his life or limb on my account." The resigned emperor was taken to Saint Médard at Soissons, his son Charles to Prüm, and the queen to Tortona. The despicable show of disloyalty and disingenuousness earned the site the name Field of Lies, or Lügenfeld, or Campus Mendacii, ubi plurimorum fidelitas exstincta est
On November 13 833, Ebbo of Rheims presided over a synod in the Church of Saint Mary in Soissons which deposed Louis and forced him to publicly confess many crimes, none of which he had, in fact, committed. In return, Lothair gave Ebbo the Abbey of Saint Vaast. Men like Rabanus Maurus, Louis' younger half-brothers Drogo and Hugh, and Emma, Judith's sister and Louis the German's new wife, worked on the younger Louis to make peace with his father, for the sake of unity of the empire. The humiliation to which Louis was then subjected at Notre Dame in Compiègne turned the loyal barons of Austrasia and Saxony against Lothair, and the usurper fled to Burgundy, skirmishing with loyalists near Châlons-sur-Saône. Louis was restored the next year, on 1 March 834.
On Lothair's return to Italy, Wala, Jesse, and Matfrid, formerly count of Orléans, died of a pestilence and, on 2 February 835, the Synod of Thionville deposed Ebbo, Agobard, Bernard, Bishop of Vienne, and Bartholomew, Archbishop of Narbonne. Lothair himself fell ill; events had turned completely in Louis favour once again.
In 836, however, the family made peace and Louis restored Pepin and Louis, deprived Lothair of all save Italy, and gave it to Charles in a new division, given at the diet of Crémieux. At about that time, the Vikings terrorised and sacked Utrecht and Antwerp. In 837, they went up the Rhine as far as Nijmegen, and their king, Rorik, demanded the wergild of some of his followers killed on previous expeditions before Louis the Pious mustered a massive force and marched against them. They fled, but it would not be the last time they harried the northern coasts. In 838, they even claimed sovereignty over Frisia, but a treaty was confirmed between them and the Franks in 839. Louis the Pious ordered the construction of a North Sea fleet and the sending of missi dominici into Frisia to establish Frankish sovereignty there.
Lothair, for the first time in a long time, allied with his father and pledged support at Worms in exchange for a redivision of the inheritance. By a final placitum issued there, Louis gave Bavaria to Louis the German and disinherited Pepin II, leaving the entire remainder of the empire to be divided roughly into an eastern part and a western. Lothair was given the choice of which partition he would inherit and he chose the eastern, including Italy, leaving the western for Charles. The emperor quickly subjugated Aquitaine and had Charles recognised by the nobles and clergy at Clermont-en-Auvergne in 840. Louis then, in a final flash of glory, rushed into Bavaria and forced the younger Louis into the Ostmark. The empire now settled as he had declared it at Worms, he returned in July to Frankfurt am Main, where he disbanded the army. The final civil war of his reign was over.
By his first wife, Ermengarde of Hesbaye (married ca 794-98), he had three sons and three daughters:
By his second wife, Judith of Bavaria, he had a daughter and a son:
By Theodelinde of Sens, he had two illegitimate children:
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