The technology of working with iron began in Ireland about 600 BC.
It is not clear when or how the Irish language arrived in Ireland.
It is not clear when or how aspects of Celtic culture arrived in Ireland.
Greek and Roman writers described the Continental Celts, several of whose artefacts and inscriptions survive.
A Celtic language was spoken in England until the fifth century AD when the languages of Germanic immigrants and invaders began to develop into what is now the English language.
The Irish converted to Christianity from the fifth century AD.
Early Christian Irish monks recorded earlier Irish myth, legend and history as well as their own religious culture in their writings.
Early Irish law was recorded by Irish lawyers called brehons.