The Gauls emerged around the 5th century BC as the bearers of the La Tène culture and migrated from Central France to the Mediterranean coast. Gallic invaders settled in the Po Valley in the 4th century BC, defeated Roman forces in a battle under Brennus in 390 BC and raided Italy as far as Sicily.

in this time they spread over much of what is now France, Belgium, The Netherlands, Spain, Portugal, Switzerland, Southern Germany, Austria, the Czech Republic and Slovakia by virtue of controlling the trade routes along the rivers of the Rhône, Seine, Rhine, and Danube, and later expanded into Northern Italy, the Balkans, Transylvania and even into Galati, (modern Turkey).

During the Balkan expedition, led by Cerethrios, Brennos and Bolgios, the Gauls raided the Greek mainland twice.

At the end of this expedition the Gallic raiders had been repelled by a coalition army of the various Greek city-states and were forced to retreat to Illyria and Thrace, but the Greeks were forced to grant safe-passage to the Gauls who then made their way to Asia Minor and settled in Central Anatolia. The Gallic area of settlement in Asia Minor was called Galatia; there they created widespread havoc. But they were checked through the use of war elephants and skirmishers by the Greek Seleucid king Antiochus I in 275 BC, after which they served as mercenaries across the whole Hellenistic Eastern Mediterranean, including Ptolemaic Egypt, where they, under Ptolemy II Philadelphus (285-246 BC), attempted to seize control of his Kingdom.

A large number of Gauls also served in the armies of Carthage during the Punic Wars, and one of the leading rebel leaders of the Mercenary War, Autaritus, was of Gallic origin.

Gaul was never united under a single ruler or government, but the Gallic tribes were capable of uniting their forces in large-scale military operations. They had the peak of their power in the early 3rd century BC.

The rising Roman Republic after the end of the First Punic War increasingly put pressure on the Gallic sphere of influence; the Battle of Telamon of 225 BC heralded a gradual decline of Gallic power over the 2nd century BC, until the eventual conquest of Gaul by Julius Caesar in the Gallic Wars of the 50s BC. After this, Gaul became a province of the Roman Empire, and the Gauls culturally adapted to the Roman world, bringing about the formation of the hybrid Gallo-Roman culture.

In the Second Punic War the famous Carthaginian general Hannibal Barca used Gallic mercenaries in his invasion of Italy. They played a part in some of his most spectacular victories, including the battle of Cannae. The Gauls were so prosperous and strong by the 2nd century that the powerful Greek colony of Massilia had to appeal to the Roman Republic for defense against them. The Romans intervened in southern Gaul in 125 BC, and eventually conquered the area known as Gallia Narbonensis by 121 BC.

In 58 BC Julius Caesar launched the Gallic Wars and conquered the whole of Gaul by 51 BC. He noted that the Gauls (Celtae) were one of the three primary peoples in the area, along with the Aquitanians and the Belgae. Caesar’s motivation for the invasion has been his need for gold to pay off his debts and to boost his political career. The people of Gaul could provide him with both. So much gold was looted from Gaul that after the war the price of gold fell by as much as 20%. While they were militarily just as brave as the Romans, the internal division between the Gallic tribes guaranteed an easy victory for Caesar. Vercingetorix’s attempt to unite the Gauls against Roman invasion came too late. After the annexation of Gaul a mixed Gallo-Roman culture began to emerge.
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The fourth-century Roman historian Ammianus Marcellinus wrote that the Gauls were tall, light-skinned, light-haired, and light-eyed:

Almost all Gauls are tall and fair-skinned, with reddish hair. Their savage eyes make them fearful objects; they are eager to quarrel and excessively truculent. When, in the course of a dispute, any of them calls in his wife, a creature with gleaming eyes much stronger than her husband, they are more than a match for a whole group of foreigners; especially when the woman, with swollen neck and gnashing teeth, swings her great white arms and begins to deliver a rain of punches mixed with kicks, like missiles launched by the twisted strings of a catapult.

The first century BCE Greek historian Diodorus Siculus described them as tall, generally heavily built, very light-skinned, and light-haired, with long hair and mustaches:

The Gauls are tall, with rippling muscles, and white of skin, and their hair is blond, and not only naturally so, but they make it their practice to increase the distinguishing color by which nature has given it. For they are always washing their hair in limewater, and they pull it back from their forehead to the top of the head and back to the nape of the neck… Some of them shave their beards, but others let it grow a little; and the nobles shave their cheeks, but they let the mustache grow until it covers the mouth.

Modern archeology strongly suggests that the countries of Gaul were quite civilized and very wealthy. Most had contact with Roman merchants and some, particularly those that were governed by Republics such as the Aedui, Helvetii and others, had enjoyed stable political alliances with Rome. They imported Mediterranean wine on an industrial scale, evidenced by large finds of wine vessels found all over Gaul, the largest and most famous one discovered in Vix Grave, which stands 1.63 m (5′ 4″) in height.

From the conquest of Gaul by Caesar, to the establishment there of the Franks under Clovis, Gaul remained for more than five centuries under Roman dominion; first under the pagan, later under the Roman Christian empire. In her primitive state of independence she had struggled for ten years against the best armies and the greatest man of Rome; after five centuries of Roman dominion she opposed no resistance to the invasion of the barbarians, Germans, Goths, Alans, Burgundians, and especially Franks, who destroyed bit by bit the Roman empire.

Gaul lived, during those five centuries, under very different Roman rules and rulers. They may be summed up under five names, which correspond with governments:

1st, the Caesars from Julius to Nero (from 49 B.C. to A.D. 68);
2d, the Flavians, from Vespasian to Domitian (from A.D. 69 to 95);
3d, the Antonines, from Nerva to Marcus Aurelius (from A.D. 96 to 180);
4th, the imperial anarchy, or the thirty-nine emperors, from Commodus to Carinus and Numerian (from A.D. 180 to 284);
5th, Diocletian (from A.D. 284 to 305).

About A.D. 241 or 242 the sixth Roman legion, commanded by Aurelian, at that time military tribune, and thirty years later, emperor, had just finished a campaign on the Rhine, undertaken for the purpose of driving the Germans from Gaul, and was preparing for Eastern service, to make war on the Persians.

The first time the name of Franks appears in history; and it indicated no particular, single people, but a confederation of Germanic peoples, settled or roving on the right bank of the Rhine, from the Mayn to the ocean. The number and the names of the tribes united in this confederation are uncertain. A chart of the Roman empire, prepared apparently at the end of the fourth century, in the reign of the Emperor Honorius (which chart, called tabula Peutingeriana, was found amongst the ancient MSS. collected by Conrad Peutinger, a learned German philosopher, in the fifteenth century), bears over a large territory on the right bank of the Rhine, the word Francia, and the following enumeration: “The Chaucians, the Ampsuarians, the Cheruscans, and the Chamavians, who are also called Franks;” and to these tribes divers chroniclers added several others, “the Attuarians, the Bructerians, the Cattians, and the Sicambrians.” Whatever may have been the specific names of these people, they were all of German race, and call themselves Franks, that is, “free-men,” and made, sometimes separately, sometimes collectively, continued incursions into Gaul, especially Belgica and the northern portions of Lyoness, at one time plundering and ravaging, at another occupying forcibly, or demanding of the Roman emperors lands whereon to settle.