Gaul

Gaul () was the name given in ancient times to the area of Western Europe that included what are now northern Italy, France, Belgium, western Switzerland and the parts of the Netherlands and Germany on the west bank of the Rhine River. Many Celtic tribes lived in the region and were known by the Romans simply as "Gauls". 

In English, the word Gaul () may mean a Celtic inhabitant of that region or all ancient speakers of Gaulish. In that way, "Gaul" and "Celt" are sometimes used in the same sense.

Gauls under Brennus attacked Rome at the Battle of the Allia (390 BC). The Romans later conquered and ruled Gaul. 

From 260 to 274, Gaul broke away from the Roman Empire and formed the Gallic Empire before it was defeated and reintegrated.

Trivia
In Greek, modern-day France is called Γαλλία (same as the Latin Gallia), and the term for a Gaulish person is  Γαλατία (Galatia).

 References 

 Other websites 
The Gallic Wars