The Celts
The Celts were a people that dominated western and central Europe during the first millenium BC. Their origins can be traced back to the Bronze Age Tumulus culture, which peaked around 1200 BC. They reached the highpoint of their power from the 5th-1st century BC, when they developed the so-called La Tene culture.

The Celts had many dealings with other cultures that bordered the lands occupied by these peoples, and even though there is no written record of the Celts stemming from their own documents, we can piece together a fair picture of them from historical accounts from other cultures.

The first historical recorded encounter of the Celts comes from northern Italy around 400 BC, when a previously unkown group of barbarians came down from the Alps and displaced the Etruscans from the fertile Po valley. These people were called Galli by the Romans and Galatai or Keltoi by the Greeks, terms meaning barbarian.

The most learned class among the Celts were the Druids, whose name means 'Knowing the Oak Tree' They seem to have frequented oak forests and acted as priests, judges, and teachers. The Druids' principal doctrine was that the soul was immortal and passed at death from one person to another. Many scholars believe that the Hindu Brahmin in the East and the Celtic Druid in the West were survivals of ancient Indo-European priesthood.

During the 1st century BC the Celts were caught between the expansion of the Roman Empire and the invasion of Germanic tribes and their world began to decline.

www link :
Celtic page about culture and languages