The People's Assembly was nervous enough about the Cimbric threat and disunity in command to reelect Marius to three successive consulships (in 104, in 103 and in 102 BC).

In 102 BC, the Cimbri returned from Hispania and, with a number of other barbarian tribes, invaded Italy.
The Teutones and their allies the Ambrones were to head south and advance toward Italy along the Mediterranean coast; the Cimbri were to attempt to cross the Alps into Italy from the north by the Brenner Pass; and the Tigurini (the allied Celtic tribe who had defeated Longinus in 107) were to cross the Alps from the northeast.
This decision proved fatally flawed.
The Germanic warriors divided their forces, making each contingent manageable, and the Romans could use their shorter lines of communication and supply to concentrate their forces at will.

First, Marius had to deal with the Teutones and their allies the Ambrones, who were in the province of Narbonensis marching toward the Alps.
He frustrated them by refusing to give battle, staying inside his heavily fortified camp fighting of their attempts to storm his fortress.
Failing to take his camp the Teutones and their allies moved on, Marius followed them waiting for an opportune moment to attack.
An accidental skirmish between Roman camp servants, getting water, and bathing Ambrones turned into a spontaneous battle between Marius' army and the Ambrones.
The Romans defeated the Ambrones with little difficulty, killing many Ambrones while losing few troops of their own.
This Roman victory caused the Teutones to halt their march and wait for Marius' army near Aquae Sextiae.
Since his opponents were waiting for him, Marius had the opportunity to reconnoiter the area and select a suitable site for the upcoming battle.
Four days after slaughtering the Ambrones, Marius marched his army onto the plain and took position on the high ground.
He had instructed his legionaries to stand their ground on the hill, launch javelins, draw their swords, guard themselves with their shields and thrust the enemy back.
He assured his men that since the barbarians would be charging uphill their footing would be unsure and they would be vulnerable.
Marius ordered his camp servants and all other non-combatants to march with the army.
He also ordered his beasts of burden to be fashioned as cavalry horses.
All of this was to create the illusion his forces were larger than they really were.
He wanted the barbarians to hold back more of their warriors in reserve so his real forces would not be overwhelmed by the tribesmen's numbers.
The surviving Ambrones and the Teutones, bent on revenge, eagerly awaited the upcoming confrontation and when the Romans finally showed themselves on the Aquae Sextiae plain they charged uphill.
The Romans unleashed a barrage of javelins, killing or maiming many tribesmen, then stood in close order, drew their swords and awaited the enemy at the top of the hill.
Roman strategy, discipline and training asserted itself and the tribesmen were unable to dislodge the legions from their superior position.
The battle continued for much of the morning, with neither side gaining the upper hand.
However, the well-conditioned and disciplined legionaries slowly and systematically forced the tribal horde down the hill until both the Romans and barbarians were on level ground.
This is when Claudius Marcellus and his 3,000 men loudly and viciously attacked the enemy rear.
The Ambrones and Teutones were now being attacked on two fronts and confusion set in, they broke ranks and started to flee, but there was no haven to be found for most of them.
The Romans relentlessly pursued them.
By the end of the afternoon, most of the barbarian warriors were dead or captured.
Estimates vary from 100,000 to 200,000 being slain or captured.
Teutobod, the Teutonic king, and 3,000 warriors escaped the battle only to be caught by the Sequani who handed them over to Marius.
Marius sent Manius Aquillius  with a report to Rome that said 37,000 superbly trained Romans had succeeded in defeating over 100,000 Germans in two engagement
The People's Assembly was nervous enough about the Cimbric threat and disunity in command to reelect Marius to three successive consulships (in 104, in 103 and in 102 BC).
In 102 BC, the Cimbri returned from Hispania and, with a number of other barbarian tribes, invaded Italy. The Teutones and their allies the Ambrones were to head south and advance toward Italy along the Mediterranean coast; the Cimbri were to attempt to cross the Alps into Italy from the north by the Brenner Pass; and the Tigurini (the allied Celtic tribe who had defeated Longinus in 107) were to cross the Alps from the northeast. This decision proved fatally flawed. The Germanic warriors divided their forces, making each contingent manageable, and the Romans could use their shorter lines of communication and supply to concentrate their forces at will.
First, Marius had to deal with the Teutones and their allies the Ambrones, who were in the province of Narbonensis marching toward the Alps. He frustrated them by refusing to give battle, staying inside his heavily fortified camp fighting of their attempts to storm his fortress. Failing to take his camp the Teutones and their allies moved on, Marius followed them waiting for an opportune moment to attack. An accidental skirmish between Roman camp servants, getting water, and bathing Ambrones turned into a spontaneous battle between Marius' army and the Ambrones. The Romans defeated the Ambrones with little difficulty, killing many Ambrones while losing few troops of their own. This Roman victory caused the Teutones to halt their march and wait for Marius' army near Aquae Sextiae. Since his opponents were waiting for him, Marius had the opportunity to reconnoiter the area and select a suitable site for the upcoming battle. Four days after slaughtering the Ambrones, Marius marched his army onto the plain and took position on the high ground. He had instructed his legionaries to stand their ground on the hill, launch javelins, draw their swords, guard themselves with their shields and thrust the enemy back. He assured his men that since the barbarians would be charging uphill their footing would be unsure and they would be vulnerable. Marius ordered his camp servants and all other non-combatants to march with the army. He also ordered his beasts of burden to be fashioned as cavalry horses. All of this was to create the illusion his forces were larger than they really were. He wanted the barbarians to hold back more of their warriors in reserve so his real forces would not be overwhelmed by the tribesmen's numbers. The surviving Ambrones and the Teutones, bent on revenge, eagerly awaited the upcoming confrontation and when the Romans finally showed themselves on the Aquae Sextiae plain they charged uphill. The Romans unleashed a barrage of javelins, killing or maiming many tribesmen, then stood in close order, drew their swords and awaited the enemy at the top of the hill. Roman strategy, discipline and training asserted itself and the tribesmen were unable to dislodge the legions from their superior position. The battle continued for much of the morning, with neither side gaining the upper hand. However, the well-conditioned and disciplined legionaries slowly and systematically forced the tribal horde down the hill until both the Romans and barbarians were on level ground. This is when Claudius Marcellus and his 3,000 men loudly and viciously attacked the enemy rear. The Ambrones and Teutones were now being attacked on two fronts and confusion set in, they broke ranks and started to flee, but there was no haven to be found for most of them. The Romans relentlessly pursued them. By the end of the afternoon, most of the barbarian warriors were dead or captured. Estimates vary from 100,000 to 200,000 being slain or captured. Teutobod, the Teutonic king, and 3,000 warriors escaped the battle only to be caught by the Sequani who handed them over to Marius. Marius sent Manius Aquillius  with a report to Rome that said 37,000 superbly trained Romans had succeeded in defeating over 100,000 Germans in two engagement
Gaius Marius