By Philip Daileader, William & Mary
In keeping with Frankish practice, Pepin divided his kingdom equally between his two sons, Charlemagne and Carloman. However, after his death, Charlemagne and Carloman edged close to war with each other. At his accession as king, Charlemagne faced resistance in his kingdom, Aquitaine. However, Carloman refused to help Charlemagne to quell the resistance, and Charlemagne seems to have retaliated by shoving Carloman out of Aquitaine entirely.

Issue of Carloman’s succession
After being shoved out of Aquitaine by Charlemagne, Carloman, suddenly and unexpectedly, died of natural causes.
Immediately, the succession of Carloman became a pressing and contested issue. He had already fathered two sons by his wife, Gerberga. Some within Carloman’s kingdom pledged their support to those children; others, though, pledged their support to Charlemagne. Gerberga and her two children fled to Italy and placed themselves under the protection of Desiderius, King of the Lombards.
It was around this time that Charlemagne dismissed his Lombard wife, who was Desiderius’s daughter. Whether Charlemagne dismissed his Lombard wife because her father was protecting Charlemagne’s nephews, or whether those nephews had fled to Desiderius because Charlemagne had already dismissed Desiderius’s daughter, is unclear.
Charlemagne, still in his early twenties, faced the pivotal moment of his entire career. He had a chance to become the one and only king of the Franks, but to do so, he would have to overcome those Franks who supported his nephews, and he would have to fight against the Lombards. And to fight against the Lombards, he would need to convince the Franks to undertake a risky crossing of the Alps.
This is a transcript from the video series Charlemagne: Father of Europe. Watch it now, on Wondrium.
The Siege of Pavia

Charlemagne succeeded in winning Frankish support for an invasion of Italy. He and his Frankish followers gathered at Geneva in the summer of 773 and agreed to invade. Charlemagne split his army in two, likely to increase speed and to make provisioning easier—these divided marches would become one of Charlemagne’s favorite maneuvers.
The Franks made it through the Alps safely; indeed, for reasons that are unclear, they encountered no resistance to speak of en route. The recombined armies besieged Desiderius in Pavia, the most important city within the Lombard Kingdom. The siege lasted for nine months.
During the siege of Pavia, Charlemagne learned that his sister-in-law Gerberga and his two nephews were not themselves at Pavia; they had taken refuge 130 miles east in Verona. Charlemagne and part of his army marched on Verona, where someone surrendered Gerberga and his nephews to Charlemagne.
Even though he now had his sister-in-law and his brother’s heirs in custody, Charlemagne continued with the siege of Pavia. Wrecked with disease, Pavia’s defenders surrendered, and Lombard resistance melted away.
In 774, Charlemagne took the title King of the Lombards and added it to his initial title, King of the Franks. He confined the deposed Lombard king, Desiderius, to a monastery in northern France, together with Desiderius’s wife and, likely, the daughter who had briefly been Charlemagne’s own second wife.
Building Connections
Charlemagne’s Lombard invasion had been a spectacular success. Not only had Charlemagne made himself the sole King of the Franks and taken possession of Carloman’s kingdom, he had toppled the two-century-old Lombard kingdom in the process, and made himself the ruler of northern Italy.

As an added benefit, Charlemagne used his invasion of Italy to reassert the Carolingian dynasty’s support for the papacy and to develop his own personal relationship with the pope.
Charlemagne traveled to Rome, the first of five visits that he would make there during his lifetime. He met with the recently consecrated Pope Hadrian I, who would remain pope for more than two decades.
And surely it is no coincidence that, from 774 onward, Charlemagne began using the title Patrician of the Romans to supplement his other titles. What did it mean to be patrician of the Romans? Nothing very specific, but the title established another conceptual link between Charlemagne and Rome. That link would continue to develop in future decades.
Military Campaigns
Charlemagne’s invasion of Italy and his war against the Lombards in 773 and 774 was just one of the many wars that Charlemagne would fight in the decades prior to his imperial coronation. In most cases, he initiated those wars.
In fact, as King of the Franks, he fought nearly every year. So rare was it for Charlemagne not to campaign that the Royal Frankish Annals specifically mention when, in a given year, he did not wage war against anyone.
His victories doubled the size of his lands, until they encompassed one million square kilometers, which is about 386,000 square miles. These campaigns required much travel on Charlemagne’s part: during the space of a single year in 785 and 786, he traveled over two thousand miles.
Charlemagne waged war in a variety of locations, and for a variety of reasons.
Common Questions about How Charlemagne Became the Sole King of the Franks
In his quest to become the only king of the Franks, Charlemagne aimed to capture the heirs of his deceased brother, to make sure there were no legitimate heirs to his kingdom except himself. They seemed to have sought refuge in the city of Pavia, and that was why Charlemagne attacked the city.
Even though he had his brother’s heirs in custody, Charlemagne didn’t stop the siege of Pavia. Eventually, the city’s defenders surrendered and Charlemagne confined the deposed Lombard king to a monastery. Now, King of the Franks was also King of the Lombards.
As King of the Franks, Charlemagne engaged in military campaigns almost every year. So rare was it for Charlemagne not to campaign that the Royal Frankish Annals specifically mention when, in a given year, he did not wage war against anyone.