The battle on the Loire of early 51 B.C. was a Roman victory that effectively ended the Great Gallic revolt on the west coast of Gaul. Although the main Gallic army had been defeated at Alesia in the previous year, the revolt continued on into the next year. The Gauls no longer attempted to form a single army that could defeat Caesar's entire force of ten legions, but instead engaged in a series of uprising on the fringes of Gaul, possibly in the hope that they would be able to wear down the Romans.
One of those uprising was led by Dumnacus, the general of the Andes tribe, who lived on the northern side of the lower Loire. Dumnacus led his army south, into the lands of the Pictones tribe, where he besieged Limonum (modern Poitiers).
The nearest Roman troops were two weak legions under Caius Caninius Rebilus, who learnt about this invasion in letters from Duracius, a Roman ally. Caninius led his legions towards Limonum, only to find that the town was besieged by too strong a force for him to attack, and that Duracius and his troops were trapped within the town. Caninius built a strong camp close to the besieged town, and wrote to Caius Fabius, who he knew was leading another two and a half legions (twenty five cohorts) into the west of Gaul.
Fabius must have approached the area from the east, perhaps following the line of the Loire. As he approached the lands of the Pictones Fabius questions a number of people who knew the area, and decided that when the Gauls discovered that Roman reinforcements were on their way they would probably abandon the siege of Limonum and attempt to reach safety by crossing a bridge over the Loire. Instead of marching directly to join Caninius he decided to head for that bridge in the hope that he could intercept the retreating Gauls.
Fabius's gamble paid off. Just as he had expected, when Dumnacus discovered that more Roman troops were on their way he decided to abandon the siege to avoid being trapped between four and a half Roman legions and the defenders of Limonum, and his route did indeed take him towards the same bridge over the Loire.
Our main source for the events of this battle, a continuation of Caesar's commentary on the Gallic Wars, written by one of his officers, suggests that the battle took place to the north of the Loire. Fabius is said to have marched to the bridge, and then sent his cavalry to chase the Gauls, but with orders to return to the main camp at the end of each day, without wearing out their horses.
The Roman cavalry caught up with Dumnacus's rearguard, although it isn't stated how many days this took, attacked them on the march and then returned to the Roman camp, greatly encouraged by the results of the first day's fighting.
That night Fabius sent his cavalry back towards the Gauls with orders to delay their march for long enough for his legions to catch them. The previous day's events played a major part in the success of this plan. When the Roman cavalry appeared for a second time the Gauls expected a second cavalry battle. The entire column halted and the infantry supported the cavalry in an attempt to destroy the Roman cavalry. The Roman cavalry was encouraged by its success on the previous day, and knowing that the legions were close behind was determined not to retreat. As a result the battle continued for long enough for Fabius and his twenty five cohorts to reach the battlefield.
The unexpected arrival of the Legions caused a panic in the Gallic army. Abandoning their baggage the Gauls attempted to flee from the battlefield, with the Roman cavalry in close pursuit. The continuation of Caesar's commentaries claims that 12,000 Gauls were killed in the chase. Another 5,000 survivors, under the command of a Senonian called Drapes, escaped from the battlefield and headed south towards the Roman province, where they became involved in one of the last major actions of the Gallic War, the siege of Uxellodunum.