The peoples known as the Celts are thought to have originated in central Europe, to the east of the Rhine in the areas now part of southern Germany, Austria, Slovakia, the Czech Republic, and Hungary. From around 3,400 years ago, these proto-Celtic peoples expanded across the Continent, and eventually inhabited a large portion of central, western, and north-western Europe. During the Classical periods of Greece and Rome, Celtic culture was predominant to the north of the Alps. Even today, Scotland, Wales, Ireland, Cornwall, Cumbria and Brittany are basically Celtic in character. Despite the changes that time has brought, the influence of Celtic tradition is still fundamental."

From "The Sacred World of the Celts" by Nigel Pennick

The Celts were a southern European people of Indo-Aryan origin who first surfaced in Bohemia and travelled west in search of the home of the sun. Science has recently established their basic blood group as 'O', in keeping with their modern descendants, which designates them as a separate race from the aboriginals of the southern Indian subcontinent, where the 'B' blood group predominates.

History tells us that there were two main Celtic groups, one of which is referred to as the 'lowland Celts' who hailed from the region of the Danube. These people left their native pastures around 1200 BC and slowly made their way across Europe, founding the lake dwellings in Switzerland, the Danube valley and Ireland. They were skilled in the use of metals and worked in gold, tin and bronze. Unlike the more familiar Celtic strain these people were an agriculturally oriented race, being herdsmen, tillers and artificers who burned rather than buried their dead. They blended peacefully with the megalithic people among whom they settled, contributing powerfully to the religion, art, and customs they encountered as they slowly spread westwards. Their religious beliefs also differed from the next group, being predominately matriarchal.

The second group, often referred to as the 'true' Celts, followed closely behind their lowland cousins, making their first appearance on the left bank of the Rhine at the commencement of the sixth century BC. These people, who came from the mountainous regions of the Balkans and Carpathians, were a military aristocracy. Reputed to love fighting for the sake of it they were frequently to be found among the mercenaries of the great armies of those early times. They had a distinct class system, the observance of which constituted one of their major racial features. These were the warlike Celts of ancient history who sacked Rome and Delphi, eventually marching victoriously across much of Europe and the British Isles.

But in spite of their martial inclinations they were also known for their qualities of chivalry, courage and dauntless bravery, their more aggressive tendencies being balanced out by a great sensitivity to music, poetry and philosophy. Unlike the lowland Celts these people buried their dead, and their elaborate religious rituals held in honour of Lugh are well recounted in the pages of the recorded past."

Pagan Celtic Spirituality understood that all of existence has a cyclic nature, and that there is a direct continuity between the material world and the otherworld. Druidic teachings, that have come down to us through Welsh tradition, recognized that there is an unseen world that interpenetrates and affects the visible world. Things are just not what they seem. Everything exists on several simultaneous levels. Human beings can understand things as having three levels: the physical, the spiritual, and the symbolic. Thus, Celtic culture was integrated with nature, and expressed itself through the multiple possibilities of life itself. Celtic religion taught the reincarnation of all individual souls, and the appearance of divine beings on Earth.

source http://www.joellessacredgrove.com/Celtic/history.html