The Gauls or Gallic people were a Celtic people living in Gaul, the region roughly corresponding to what is now France, Belgium, Switzerland the parts of the Netherlands and Germany on the west bank of the Rhine, and the western parts of Northern Italy, from the Iron Age through the Roman period. They mostly spoke the Continental Celtic language called Gaulish and dominated West-Central Europe from the 5th to the 1st centuries BC.
Gaulish culture developed out of the Celtic cultures over the first millennia BCE. The Urnfield culture (c. 1300 BCE – c. 750 BCE) represents the Celts as a distinct cultural branch of the Indo-Europeans. The spread of iron working led to the Hallstatt culture in the 8th century BCE; the Proto-Celtic may have been spoken around this time. The Hallstatt culture evolved into the La Tène culture in around the 5th century BCE. Following the climate deterioration in the late Nordic Bronze Age, Celtic Gaul was invaded in the 5th century BCE by tribes later called Gauls originating in the middle Rhine river valley. Gallic invaders invaded defeated Roman forces in a battle circa 390 BCE and raided Italy as far as Sicily, later settling large parts of the Po valley in the 3th century BC. 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 Anatolia. 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 and by invading Germanic tribes. During the crisis of the third century, there was briefly a breakaway Gallic Empire founded by the Batavian general Postumus. By the arrival of the Franks during the Migration Period (5th century), the Gaulish language had been replaced by Vulgar Latin.