The Celts affected many European cultures. However they have a particular importance for the Irish as they are predominantly the people that the Irish have descended from. But who were they?

The Celts originated c. 1500 BC during the Bronze Age. They were the first Indo-European peoples to spread throughout Europe. They probably originated in present-day France, S Germany. By 550 BC Celtic culture is endemic throughout Britain, France, Western Spain, South Germany, North Italy and stretching East to the Black Sea. There is even a group in Central Turkey (the Galatians, who St. Paul writes to in the New Testament). There is trade between the Celts and the Etruscans. In 400 BC the Celts cross the Alps and invade Italy and ten years later sack Rome. They demand a large bounty of gold. In 335 Celts meet Alexander the Great, the same year as he destroys Thebes. He is impressed by them as warriors. However it is around now that the Celts begin to decline as a force and in 230 BC the Galatians are defeated by the Greeks. In 225 they are defeated by the Romans at the battle of Telamon in Italy. In 125 Rome conquers Southern Gaul. From this point on the Celts were never to be a real force in Europe again. Celtic tradition survived most and for longest in Ireland and Britain. They were famous for their burial sites and hill forts, and their bronze and iron art and jewellery. Their modern descendents are found chiefly in Ireland, Scotland, and Wales.

The language spoken by the Celts was Celtic. There were two main branches: Goidelic comprises the Gaelic spoken in Ireland, which spread to the Isle of Man and Scotland; Brythonic (also called Brittonic or British) comprises Welsh, Cornish, and Breton. The are some dialects spoken on the continent, known as Continental Celtic (Gaulish in France, Celtiberian in Spain and Insular Celtic in Brittany).