Irish Celts
The tribes of Celtic speech came to the British Isles in two distinct waves. The earlier invasion of the Goidels arrived in England with a culture of bronze about 800 B.C., and in Ireland two centuries later, and was part of the same movement which brought the Gauls into France. The later conquest was by the Cymric-speaking Belgae who were equipped with iron weapons. It began in the third century B.C., and was still going on in Caesar’s time. These Cymric Brythons reached Ireland in small numbers only in the second century B.C.
Source: various