4000-2500 BCE Neolithic Britain / The Stone Age
c. 3000 BCE Newgrange (Brú na Bóinne) built
2000-3000 BCE Stonehenge built
2500-1500 BCE Most other pre-Celtic megaliths built
2500-800 BCE The Bronze Age in Britain
1300-700 BCE Existence of the proto-Celtic Urnfield Culture
800 BCE – 50 CE The Iron Age in Britain
700-450 BCE The Halstatt period (first ‘true’ Celtic culture)
500-15 BCE The La Tène period. The Heroic Age/Ulster Cycle.
390 BCE Celtic invasion of Rome
c. 200 BCE Fenian Cycle from Irish mythology
279 BCE Celtic invasion of Greece
100 BCE Arrival of Gaels in Ireland
82 BCE Rome repels the Celts
70 BCE First known appearance of the Druids
55 BCE Romans invade Celtic Britain (under Julius Caesar)
52 BCE Rome defeats the Celts in Gaul
43 – 409 CE Rome controls Celtic territories in Britain
61 CE Rome destroys last remaining Druid communities
62 CE Queen Boudicca defeated, Iceni rebellion ends
432 CE Patrick brings Christianity to Ireland
465 CE Probable birth of the historical Arthur
563 CE Arrival of Columcille in Iona
793-1050 CE The Viking Age in Britain
c. 800 CE The Book of Kells written
1066 Norman invasion of Britain
c. 1100 CE The Book of Invasions, Lebor Gabála Érenn, written
BCE – Before Common Era
CE – Common Era
Sources:
‘The Everything Celtic Wisdom Book’ Jennifer Emick
Wikipedia
The Celtic Journey 