The Celts had a great impact on Ireland history.Irish History Timeline #"justify">.Ireland and it's Viking influence.Popular history of Ireland.The relative density of very early sites in Ulster suggests western Scotland as a starting point.Out of 100 found in Europe 80 of them were in Ireland.This was the time when the Celts came to Ireland - probably not peacefully but as an invading force.They came as different groups or tribes taking control of different areas in Ireland.The Celts arrived in Ireland approximately 700BC and continued their migration until about 400AD.This was called ORahillys historical model and could give us some understanding of Irelands Celts.It was also around the same time the La Tène culture may have been introduced to Ireland.