They were most of the population in Gallia, today's France, Switzerland, possibly Belgica – far Northern France, Belgium and far Southern Netherlands, large parts of Hispania, i.e. Iberian Peninsula – Spain and Portugal, in the northern, central and western regions; southern Central Europe – upper Danube basin and neighbouring regions, large parts of the middle Danube basin and the inland region of Central Asia Minor or Anatolia.
They lived in these many regions forming a large arc stretching across from Iberia in the west to the Balkans and Anatolia in the east.
Classical Antiquity authors did not describe the peoples and tribes of the British Islands as “Celts” or “Galli” but by the name “Britons”.
[1] Source:[2] They lived in Southern Central Europe (in the Upper Danube basin and neighbouring regions) which is hypothesized as the original area of the Celts (Proto-Celts), corresponding to the Hallstatt Culture.
Later they expanded towards the Middle Danube valley and to parts of the Balkans and towards inland central Asia Minor or Anatolia (Galatians).
Hercynian Forest (Hercynia Silva), north of the Danube and east of the Rhine was in their lands.
These people, called Galatians, a generic name for “Celts”, were eventually Hellenized,[22][23] but retained many of their own traditions.
Galli (Gauls), for the Romans, was a name synonym of “Celts” (as Julius Caesar states in De Bello Gallico[25]) which means that not all peoples and tribes called “Galli” were necessarily Gauls in a narrower regional sense.
They seem to have been an older group of Celts that lived in Cisalpine Gaul before the Gaulish Celtic migration.
Eastern Iberian meseta (Spain), mountains of the headwaters of the rivers Douro, Tagus, Guadiana (Anas), Júcar, Jalón, Jiloca and Turia, (tribal confederation).
There were three or four distinct Celtic populations in these islands, in Britannia inhabited the Britons, the Caledonians or Picts, the Belgae (not surely known if they were a Celtic people or a distinct but closely related one); in Hibernia inhabited the Hibernians or Goidels or Gaels.
Classical Antiquity authors did not call the British islands peoples and tribes as Celts or Galli but by the name Britons (in Britannia).
According to Ptolemy's Geography (2nd century AD) (in brackets the names are in Greek as on the map): Para-Celtic has the meaning that these peoples had common ancestors with the Celts but were not Celts themselves (although they were later Celticized and belong to a Celtic culture sphere of influence), they were not direct descendants from the Proto-Celts.
Because of the strong Celtic influences on their language and culture, they were known already in antiquity as Celto-Ligurians (in Greek Κελτολίγυες, Keltolígues).
Today's Western Andalusia (Hispania Baetica), Baetis (Guadalquivir) river valley and basin, Marianus Mons (Sierra Morena), some consider them Celtic,[43] may have been Pre-Celtic Indo-European people as the Lusitani and Vettones.
They lived in the Central Alps, eastern parts of present-day Switzerland, the Tyrol in Austria, and the Alpine regions of northern Italy.