Gaul (Latin: Gallia), an ancient region of western Europe. Gaul in Julius Caesar's time included most of northern Italy (Cisalpine Gaul), which was occupied by the Romans, and the vast extent of territory from the Rhine River to the Pyrenees called Transalpine Gaul (Gaul beyond the Alps), which was largely inhabited by Celts. Transalpine Gaul included what is now France and Belgium and parts of Switzerland, Germany, and the Netherlands. Knowledge of the region and the Celts comes mainly from Caesar's Commentaries on the Gallic War. He says in the opening of his book that Gaul (meaning Transalpine Gaul) was divided into three parts—Aquitania in the southwest, Gallia in the center, and Belgica in the northeast.Gaul. The Transalpine territory of Gaul consisted of what are now France, Belgium, Luxembourg, Germany west of the Rhine River, and the Netherlands south of the Rhine. The Cisalpine territory of Gaul covered the northern part of the Italian peninsula.
The Gauls sacked Rome in 390 B.C. , but by 192 B.C. Rome had become sufficiently strong to bring all of Cisalpine Gaul under its control. By 51 B.C. Caesar had conquered the heart of Gaul, or France.