The Gauls were a Celtic people living in Gaul, the region roughly corresponding to what is now France, Belgium, Switzerland and Northern Italy, from the Iron Age through the Roman period. They mostly spoke the Continental Celtic language called Gaulish.

Gauls under Brennus defeated Roman forces in a battle circa 390 BCE. The peak of Gaulish expansion was reached in the 3rd century BCE, in the wake of the Gallic invasion of the Balkans of 281-279 BCE, when Gaulish settlers moved as far afield as Asia Minor.

Archaeologically, they were the bearers of the La Tène culture (5th to 1st centuries BCE). In the 3rd century BCE, the Gauls expanded towards the southeast in a series of invasions, including the Gallic Invasion of Greece, with a few settling as far east as Anatolia, as the Galatians. They were conquered by Julius Caesar in the Gallic Wars in the 50s BCE, and during the Roman period became assimilated into a Gallo-Roman culture. During the crisis of the third century, there was briefly a breakaway Gallic Empire under Postumus, Marcus Aurelius Marius and Tetricus I. By the arrival of the Franks during the Migration Period (5th century), the Gaulish language had been replaced by Vulgar Latin.

Gaius Julius Caesar (Classical Latin: [ˈɡaː.i.ʊs ˈjuː.lɪ.ʊs ˈkaj.sar], July 100 BC – 15 March 44 BC) was a Roman general and statesman and a distinguished writer of Latin prose. He played a critical role in the gradual transformation of the Roman Republic into the Roman Empire.

In 60 BC, Caesar, Crassus and Pompey formed a political alliance that was to dominate Roman politics for several years. Their attempts to amass power through populist tactics were opposed by the conservative elite within the Roman Senate^{[citation needed]}, among them Cato the Younger with the frequent support of Cicero. Caesar's conquest of Gaul, completed by 51 BC, extended Rome's territory to the English Channel and the Rhine. Caesar became the first Roman general to cross both when he built a bridge across the Rhine and conducted the first invasion of Britain.

These achievements granted him unmatched military power and threatened to eclipse Pompey's standing. The balance of power was further upset by the death of Crassus in 53 BC. Political realignments in Rome finally led to a standoff between Caesar and Pompey, the latter having taken up the cause of the Senate. Ordered by the Senate to stand trial in Rome for various charges, Caesar marched on Rome with one legion—legio XIII—from Gaul to Italy, crossing the Rubicon in 49 BC. This sparked a civil war from which he emerged as the unrivaled leader of the Roman world.

The Gallic Wars were a series of military campaigns waged by the Roman proconsul Julius Caesar against several Gallic tribes. They lasted from 58 BC to 50 BC and culminated in the decisive Battle of Alesia in 52 BC, in which a complete Roman victory resulted in the expansion of the Roman Republic over the whole of Gaul. The wars paved the way for Julius Caesar to become the sole ruler of the Roman Republic.

Although Caesar portrayed this invasion as being a preemptive and defensive action, most historians agree that the wars were fought primarily to boost Caesar's political career and to pay off his massive debts. Still, Gaul was of significant military importance to the Romans, as these had been attacked several times by native tribes both indigenous to Gaul and farther to the north. Conquering Gaul allowed Rome to secure the natural border of the river Rhine.

The Gallic Wars are described by Julius Caesar as himself in his book Commentarii de Bello Gallico, which is a pertinent and only slightly tendentious and altogether the most important historical source regarding the conflict.