The largest, bloodiest, and most destructive battle of the ninth century began at 6 in the morning on Saturday, June 25, 841, at Fontenoy-en-Puisaye, now a tiny village 22 miles (35 kilometers) south of Auxerre in France. Exactly how many men took part is uncertain. We know that probably between 25,000 and 30,000 were killed and many more injured, which indicates large armies and extreme violence. This battle was fought as part of what German historians call the Brüderkrieg, “brother war.” Emperor Lothar fought on one side against his brother Louis the German and their half-brother Charles the Bald on the other. All were sons of Louis the Pious, and this was just one incident in the long civil war fought between them. The battle signaled the end of any possibility of restoring the unified empire stretching across France, Germany, the Benelux countries, Italy, and northern Spain that the three combatants’ father, Louis the Pious, had inherited from his father, Charlemagne. After the Battle of Fontenoy, the possibility of an ordered state and good government vanished in Western Europe.

The battle didn’t have to end in such bloodshed. According to Nithardus’s reliable Four Books of Histories, Charles and Louis had spent the previous three days negotiating with Lothar, begging him “to remember that they were brothers . . . [and] asking him ‘to leave the Church of God and the whole Christian people in peace.’” They offered him generous terms. Nithardus, a well-educated public official and soldier in the service of Charles the Bald, says that Lothar equivocated. Pretending to consider Charles and Louis’s pleas, he was actually playing for time, awaiting the arrival of troops under Pippin II of Aquitaine. Once Pippin arrived, Lothar broke off negotiations. So “Louis and Charles rose at dawn, occupied the peak of a mountain [it was actually a low hill] near Lothar’s camp . . . and waited for Lothar’s arrival and the striking of the second hour [6 a.m.]. . . . When both had come they fought a violent battle.”

The actual battlefield was a flat expanse surrounded by low hills. There seem to have been two interrelated fronts, as Charles and Louis attacked Lothar from separate low hills. Leading any of the armies at Fontenoy would have been difficult because tenth-century armies were not the highly organized and disciplined forces with clear lines of authority that we know today. The emperor or king would have been the overall leader, but his armies were made up of diverse units led by local warlords. Unused to cooperation with others, some of whom would have previously been their enemies, warlords would have found it difficult to submit to the king’s instructions. The desire to achieve glory by exhibiting heroics would have been far stronger than any sense of discipline and obedience to the commander. Even though well trained and in good physical condition, the foot soldiers as well as the warlords would have been psyched up to enhance their reputation as warriors.

Tactics in this era were generally consistent from battle to battle. Action would begin with the terrifying war cries of foot soldiers. The core of the infantry was the Heerbann, a kind of trained militia. They usually opened the battle by moving forward in close formation protected by a strong shield wall. Their basic weapon was a long-handled throwing ax. Some wore light armor and used a stabbing sword. When the commander decided the time was right, he would order a mass charge of mounted knights, or any man who could afford a horse. Wearing body armor and carrying a spear as their primary offensive weapon and a shield for defense, the mounted troops usually rode sturdy Barb horses, a strong, wiry breed with a fiery temperament and good turn of speed, ideal for cavalry charges. Large massed cavalry charges would be followed by the kind of mounted hand-to-hand conflict between horsemen with swords that led to many of the injuries and deaths.

The Battle of Fontenoy proceeded indecisively for hours. It wasn’t until about noon that finally a cavalry charge broke through Lothar’s lines. This was followed by the bulk of the slaughter, in which many of the elite of the Frankish nobility were killed. According to the Annals of Saint-Bertin (which was sympathetic to Louis and Charles), “Many were slain on both sides; still more were wounded. Lothar suffered a shameful defeat and fled. The slaughter of fugitives continued . . . until Louis and Charles, aflame with generous feelings, ordered an end to the carnage.”

Nithardus, who fought in the battle, says, “The booty and slaughter were immense and truly astonishing.” According to his telling, Charles and Louis “ceased fighting and plundering and returned to camp . . . to talk over what they ought to do next.” Next day they celebrated Mass, and the bishops who accompanied the armies asked for prayers and a three-day fast for the remission of the sins of both sides. While violent in combat, Frankish foot soldiers were otherwise generally well disciplined, sober, and religious, believing that God was on their side. They were supported by a well-organized commissariat. Accompanying this was a bevy of camp followers, including merchants who supported the army with supplies and brought women who prepared food and did other tasks and who acted as prostitutes when needed. The merchants always defended their supplies, and they were notorious for being drunken, lecherous, and foul-mouthed.

Fontenoy was unlike modern battles. It was not the impersonal, industrial-style modern warfare of World Wars I and II. It was man-to-man, one-on-one combat with long (5-foot, or 1.5-meter) and short (3-foot, or 1-meter) swords, spears, and lances (6 feet, or 2 meters), daggers (6 inches to 1 foot long), and crossbows and hand axes, all weapons that inflicted terrible wounds. Alain Mounier Kuhn has examined many medieval sources describing wounds and has found that more than half were to head, face, and neck. The most effective weapons were lances, swords, and bows and arrows. Body armor seems to have protected the torso, so most injuries were to the upper body, and Kuhn says that many injuries seem to have been sustained when soldiers were unable to defend themselves. It was personal and brutal, kill or be killed. Part of the explanation for this kind of fighting was that people then were much more easily stirred up emotionally, violence was more generally accepted, and, as noted earlier, personal self-control was in short supply. Also, a warrior satisfied his lust for glory by killing, while at the same time believing that God was on his side. And given the nature of the weapons used (with the exception of longbows or crossbows), the only way the warrior could kill someone was up close and personal. Many also died soon afterward of the terrible slashing wounds inflicted, especially in light of ninth-century medicine. For many it would have been better to have been killed outright.