The story of the Celts began 5,000 years ago in the nomadic steppes of Central Asia when the Kurdan people tamed the horse and then began a southward trek first into the Caucasus (Around 2400 BC) where the Indo European culture emerged, then into Anatolia from whence arose the mighty Hittite empire and then finally around 1800 BC into the Baltic regions, into what is now Eastern and Central Europe where the Unetice culture began.
From that migration in the mid Bronze Age emerged the Italians, the Venetians, the Illyrian, and the Celtic people, who went on to reach Hibernia.
One continuous migration then that pushed out originally from Central Asia some 2,500 years later found itself poised on the rim of the Mediterranean, the region of the south, the land of sun, around 1000 BC.
The Latin branch of the Celtic family poured southwards across the Alps and claimed sunny fertile Italy and created a Roman civilization.
There were wars, alliances, victories, and defeats and in the end the Romans an offshoot of the same originating stock from which the Northern Celts had come, took full possession of the Italian peninsula. After the defeat of Carthage the Romans became completely dominant.
Stuck in the North the Celts marked up on 800-year trek seeking to invade sunnier lands. The Celts of old always looked southwards. They sacked Rome in 390 BC and later when Hannibal crossed the Alps and drove towards Rome Celtic tribes accompanied him but both were defeated by Rome.
Around 175 BC the Romans drove the Celts out of Italy finally.
Under Julius Caesar the Romans conquered the troublesome Celts after crossing the Alps and enforced the disciplines of order and might. The Celts brought the gifts of lyricism imagination and religious wonder.
The Roman empire outside Rome itself was Iberia, Galicia and Gaul and was heavily Celtic. After the conquering of Britain only the Celts of Hibernia remained. Then came Patrick.
That is where we have descended from.