Though the Celts are commonly thought to be the ancient Irish, they in reality covered a much larder area with their civilization.
The Celts' first appearance in history shows them coming out of the East in waves of migrants in the 9th Century, BC, spreading into Gaul, Northern Italy, Asia Minor, Britain, Scotland, Wales, Ireland, the Balkans, and the Iberian Peninsula. They were sacking town in Italy, France, Germany and Switzerland by the 5th Century, areas where they settled for a time. At the height of their power, their territory reached from the British Isles to Turkey, but they finally fell to both the Romans and the Germanic tribes.
They spoke dialects of the same language, though they were not all from the same ethnic background, and they were among the greatest technologists of the ancient world with skilled metal workers, builders of roads and chariots, experts in agriculture and
Animal breeding, and they were warriors of unparalleled courage and ferocity (they were feared by even the Roman legions), laying the foundations of Western Civilization.
The Celts were a brilliant, flamboyant, fearless and dynamic people, but were also given to drunkenness and boasting. The women were held in high regard, and as good warriors of their men. A Celtic women, with her temper aroused, was a dangerous force, and it wasn't unusual for them to fight alongside their men.
By the beginning of the 1st Century BC, the Romans began to encroach on the Celtic territories, eventually conquering most of their lands, with the exception of Scotland and Ireland. although there were still sporadic uprising, and one lead by Queen Boadicia in Britain (around 61 AD) nearly wiped out the Roman legions in the country there. The Celtic belief wasn't destroyed until the Christians began to come inroads, following on the heals of the Romans already there.
Around 600 BC, the Celts invented an Alphabet, called the Ogham (pronounced "owam") that was used for special recordings, and known by the Druids. They Druids also knew and used the Greek Alphabet, which they put in use for ordinary messages, and the later Bards of Wales continued the Ogham to record what they could remember of the Druidic traditions. The Christian church eventually forcibly replaced this writing with the Latin alphabet, and it is likely they at some point (probably in Ireland), with the knowledge of these three alphabets, the Celts began to record their history and legend. And although it’s believed that the Celts kept no written records, St. Patrick personally burned almost 200 Irish books written in the Celtic Language, setting an example for Christian zealots, who destroyed every bit of Druidic literature they could find. But, for some unknown reason, the Christian monk-scribes felt compelled to record the Celtic myths, even while the missionaries were determinately stomping out the belief in the ancient gods and goddesses.