500- La Tene Period. (Heroic age of the Celts, 15 BCE time of mythology)
450 BCE Celts expanded into Spain. Anglo-Saxon invasion.
400 BCE The Celts had nomadically migrated into northern Italy.
387 BC: Battle of the Allia and subsequent Gaulish sack of Rome.
340 BC Roman commanders are forbidden to settle warfare by single combat with Celtic Chieftains.
335- Celts encounter Alexander the Great, King of Macedonia, on the Danube. They exchange pledges of alliance. Large numbers of Celtic warriors join the Greeks in a war against the Etruscans.
390 Gauls defeat Roman army : battle of the Allia sack of Rome by the Gauls
285 Further Celtic hostilities against Rome; massacre on the River Tiber.
279 Celts invade Greece through Macedonia, temple of Delphi plundered.
270 Celts moved in to Galatia
225 BC: 225 BC Battle of Telemon; Celts advance on Rome again. Roman army routs invading Celtic Gauls at Telamon in central Italy, all Celtic tribes south of River Po destroyed. From the major Celtic loss at the Battle of Telamon, Celtic lands come under pressure from the Germanic tribes to the north, and the spread of Rome. Gallia Cisalpina and southern Gaul are conquered; the Iberian Peninsula falls by degrees.
218 Second Punic War begins. Hannibal with Celtic mercenaries makes his famous Alpine crossing to invade Italy, the Roman heartland.
216 Hannibal famously crushed the Roman legions at the Battle of Cannae.
202 Hannibal defeated at Zama by Scipio; extensive Romanization of Celtic tribes begins.
200 The Celts occupied the British Isles, Brittany, modern France, Netherlands, Belgium, Germany, and Switzerland.