4000-3500 B.C.E. and earlier The future Celtic territories are first farmed, and megalithic monuments are built

2500-1500 B.C.E. Period during which most pre-Celtic megaliths were built

1800-1600 B.C.E. The Bronze Age

1000 B.C.E. The appearance of the proto-Celtic Urnfield Culture

900-500 B.C.E. The Halstatt period — emergence of the first true Celtic culture

600 B.C.E. Iron Age

500-15 B.C.E. The La Tène Period, exemplified by an explosion of art and culture. Also referred to as the Heroic Age.

450-450 B.C.E. Expansion of Celtic culture into Spain and Northern Italy

390 B.C.E. The Celtic invasion of Rome

279 B.C.E. Celts invade Greece

200 B.C.E. Gaulish occupy many parts of Western Europe, including the British Isles, France, Germany, Belgium, and Switzerland

100 B.C.E. Arrival of the Gaels in Ireland

82 B.C.E. Rome repels the Celts

70 B.C.E. First known appearance of the druids

55 B.C.E. The Romans under Julius Caesar invade Celtic Britain

52 B.C.E. Rome defeats the Celts in Gaul

43 B.C.E.-409 C.E. Roman control of Celtic territories in Britain and Wales

61 C.E. Rome destroys remaining druid communities at Anglesey

62 C.E. Queen Boudicca defeated and the Iceni rebellion ended

432 C.E. Arrival of St. Patrick brings Christianity to Ireland

445 C.E. Vortigern and Myrddn

465 C.E. Probable birth of the historical Arthur

563 C.E. Arrival of Columcille in Iona