The location of the final battle between the Aedui and their enemies, which Caesar names as the Battle of Magetobriga, remains unknown, but Ariovistus’ fifteen thousand men turn the tide, and the Aedui become tributary to the Sequani.

Cicero will write in 60 BCE of a defeat sustained by the Aedui, perhaps in reference to this battle.

Ariovistus seizes a third of the Aeduan territory, settling one hundred and twenty thousand Germans there.

In order to avoid infringing on his allies for the moment, Ariovistus must have passed over the low divide between the Rhine and the Doubs in the vicinity of Belfort and then have approached the Aedui along the Ognon river valley.

That move leaves the Sequani between him and the Jura mountains, not a tolerable situation for either if they are not going to be allies.

Ariovistus makes the decision to clear out the Sequani from the strategic Doubs valley and repopulate it with Germanic settlers.

He demands a further third of Celtic land for his allies the Harudes.

Caesar makes it clear that Germanic tribes are actually in the land of the Sequani and are terrorizing them.

They are said to have controlled all the oppida, but this statement is not entirely true, as Vesontio is not under Germanic control.

Presumably, the country to the north of there is under Germanic control.

By the end of the campaign, the non-client Suebi, under the leadership of Ariovistus, stand triumphant over both the Aedui and their co-conspirators.

Rome, fearing another mass migration akin to the devastating Cimbrian War, and now keenly invested in the defense of Gaul, will be drawn irrevocably into war.

The Sequani reward Ariovistus with land in 61 BCE following his victory in the Battle of Magetobriga.

Ariovistus settles the land with one hundred and twenty thousand of his people.

When twenty-four thousand Harudes join his cause, Ariovistus demand that the Sequani give him more land to accommodate the Harudes people.

This demand 'concerns' Rome because if the Sequani concede, Ariovistus will be in a position to take all of the Sequani land and attack the rest of Gaul.

By this time, the Helvetii are well on their way in the planning and provisioning for a mass migration under the leadership of the wealthy aristocrat Orgetorix, who has persuaded the Helvetians to attempt to migrate from Helvetian territory to southwestern Gaul (modern-day France).

The reasons for their migration are mentioned by Caesar in separate passages as either harassment by the Germanic tribes, or not being able to in turn raid for plunder themselves due to their situation in hilly and mountainous territory.

Via council and parley, Orgetorix makes clandestine negotiations with the ambitious Sequani and the Roman-dominated Aedui.

The Sequani are beginning to resent and regret the abundance of unruly Germanic war bands and their huge encampments of dependents.

The Aedui are loath to obey the Roman spur any longer than they must and are keen to revisit their former days at council.

The parley for the trek is successful and Orgetorix is granted passage, and with the trek ratified by council, an army is called up and provisioned.

During this process, Orgetorix had also succeeded in making a personal alliance with the Sequanii chieftain Casticus and the Aedui chieftain Dumnorix through marital arrangements and host exchange of family members.

Orgetorix's Gallic rivals allege that these political successes and displays of diplomacy are intended to benefit Orgetorix alone and their claims are made more convincing by Roman intrigues and impositions.

The majority of the Gallic tribes congratulate Caesar following his victory over the Helvetii, and seek to meet with him in a general assembly.

Diviciacus, the head of the Aeduan government and spokesmen for the Gallic delegation, expresses concern over Ariovistus’ conquests and the hostages he has taken.

Diviciacus demands that Caesar defeat Ariovistus and remove the threat of a Germanic invasion otherwise they would have to seek refuge in a new land.

Not only does Caesar have a responsibility to protect the long-standing allegiance of the Aedui, but this proposition presents an opportunity to expand Rome’s borders, strengthen the loyalty within Caesar’s army and establish him as the commander of Rome’s troops abroad.

As the Senate had declared Ariovistus a “king and friend of the Roman people” in 59 BCE, Caesar cannot declare war on the Suebi tribe.

Caesar, saying that he cannot ignore the pain the Aedui have suffered, delivers an ultimatum to Ariovistus demanding that no German cross the Rhine, the return of Aedui hostages and the protection of the Aedui and other friends of Rome.

Although Ariovistus assures Caesar that the Aedui hostages will be safe as long as they continue their yearly tribute, he takes the position that he and the Romans are both conquerors and that Rome has no jurisdiction over his actions.

With the attack of the Harudes on the Aedui and the report that a hundred clans of Suebi are trying to cross the Rhine into Gaul, Caesar has the justification he needs to wage war against Ariovistus in 58 BCE.

Learning that Ariovistus intends to seize Vesontio, the largest town of the Sequani, Caesar commences marching his troops toward Vesontio.

Some of Caesar’s officers hold their posts for political reasons only and have no war experience.

As a result, they suffer from poor morale which threatens Caesar’s campaign.

Caesar challenges the officers and their legions, saying that the only legion he can trust is the Tenth.

With their pride on the line, the other legions follow the Tenth’s lead, determined not to be outdone.

Consequently, Caesar arrives in Vesontio before Ariovistus.

They meet and rout the Germanic army in the land between the city and river, effecting a massacre as the Germans try to escape over the river.

Most of Ariovistus’ hundred and twenty thousand men are killed.

Some, including Ariovistus himself, manage to cross the river in boats or by swimming.

The rest are cut down by Roman cavalry, including both of Ariovistus's wives and one of his daughters; another daughter is taken prisoner.

Ariovistus and what remains of his troops escape and cross the Rhine, never to engage Rome in battle again.

Both Caesar's emissaries are rescued unharmed, to relate their harrowing adventures as the Germans debated (in their presence) whether they should be burned then or later.

Caesar said that encountering Procillus and freeing him from his chains gave him as much pleasure as the victory, which offers some insight into the emotional climate of Caesar's forces; the officers were a sort of family.

The fate of the twenty-four thousand Harudes is not known.

The Suebi encamped near the Rhine return home.

Caesar is victorious.

Many of the Boii tribe, after defeat at Roman hands in the late second century BCE, had fled north across the Alps from northern Italy into an area called Boihaemum by the Romans, which includes the southern part of present-day Bohemia.

The western half is conquered and settled from the first century BCE by Germanic (probably Suebic) peoples including the Marcomanni; the elite of some Boii then migrate west to modern Switzerland and southeastern Gaul.

Those Boii that remain in the eastern part will eventually be absorbed by the Marcomanni.

The only ancient reference to the agri decumates comes from Tacitus' book Germania.

A region of the Roman Empire's province of Germania superior ("Upper Germany"), the agri decumates or decumates agri cover the Black Forest area between the Main river and the sources of Danube and Rhine rivers, presently in southwestern Germany (modern Wurttemberg, Baden and Hohenzollern).

To the southeast, the decumates border the militarily important province of Raetia.

The meaning of decumates is lost and has been the subject of much contention.

According to the English Classicist Michael Grant, the word probably refers to an ancient Celtic term indicating the political division of the area into "ten cantons."

According to Tacitus, the region had originally been populated by the Celtic tribe of the Helvetii but soon Germanic Suebi, possibly under Ariovistus, had settled there before migrating around 9 BCE to Boiohaemum (modern day Bohemia).

After the Suebi leave, the area is again inhabited by Gauls.