The Celts

The ancient Celts were various population groups living in several parts of Europe north of the Mediterranean region from the Late Bronze Age onwards. Given the name Celts by ancient writters, these tribes often migrated and so eventually occupied territories from Portugal to Turkey. Although diverse tribes the ancient Celts spoke the same language and maintained the same artistic tradition which is characterised by the use of idiosyncratic flowing lines and forms. Celtic language are still spoken today in parts of the British Isles an northen France.

Celtic Tribal Culture

That said, the Celts would never have described themselves as a "nation". Although linked to some degree by a common language, similar pagan gods, expertise in iron, and similar forms of cultural expression, their communities were so extended across Europe, that there was no realistic possibility of cohesion or unity under any form of central authority. And they were as likely to fight each other as any outsider. This lack of unity would, in time to come, make them extremely vulnerable to the smaller but better organized military state of Rome.

To give you an idea of the multiplicity of tribal societies which were associated with Celtic culture, here is a brief guide to the vast array of Celtic tribes and clans active in Iron Age Europe during the period 500-55 BCE, based on archeological excavations and written accounts by Greek/Roman historians.

Celtic Warriors
For hundreds of years, the Celtic warrior represented the quintessential barbarian warrior to the settled peoples of the Mediterranean. To the Romans, Greeks and other "civilized" people, the Celts where a re-occurring nightmare that unpredictably erupted from darker Europe. It was a wellearned reputation, and they repeatedly gave the Mediterranean world reason to fear them. Celtic warriors stood a head taller than their Mediterranean opponents and are described as having muscular physiques. The celtic warriors, or Gauls as they were called in the French part of their range, spiked their hair up with lime and wore horned and winged helmets to emphasize their large stature. Their attacks on thd battlefield were fearless, wild and savage, but they were also skilled and deadly. As the Celts spread over their vast range, having conquered most of Europe at their height, their warriors developed different styles of warfare. In Spain, they became master swordsmen accustomed to up-close combat with their short swords. In southern Gaul they developed impressive armor and preferred long swords, while in Britain they continued to fight from chariots that they had adapted to rough ground. However, whether in Asia Minor or Ireland, the Celtic warrior remained essentially the same, a capable warrior and someone to be feared. This was a fact Romans never forgot, as it had been forever planted in their psyche when the young republic was sacked by the Celtic warchief Brenus. The effect this had on the Romans changed history as they poured their energies into their military with single-minded focus that would eventually win them an empire.
Celtic Warrior Culture 
The Celts were a warrior culture. Fighters were admired like heroes and courage in the battleground was an important virtue. The Celtic elite fighters functioned as models, which should inspire other warriors by their courage.
The celts cut off the heads of killed enemies and collected them. It as considered a spiritual gesture, which often also appears in other cultures. The head was valued by the Celts as the seat of life, emotions and the soul. He who had captured a head attained the strength of the fallen enemy. Such trophies were bound to their horse or fastened to their belts, a practice that also served to cause fear in their enemies.
One of the main motivations of Celtic warrios was the persuit of glory and to this end the Celts loved exhibition when in battle. Thus there are legends of a Celtic ruler who drove a silver chariot into battle. Naturally silver is very soft and rather unsuitable for a chariot, but the hostile war bands took to flight at the sight of it. Warriors often painted themselves with woed, a blue die, or used war cries in order to intimidate their enemies. Celtic warriors would also wear horned helmets or helmets topped with horse tails into the battle to intimidate their enemies and make themselves appear taller. A helmet was found crowned with a metal raven. When the wearer ran the metal wings of the raven would flap and stike the helm. This is an allusion on the Celtic mythology in which the death goddess gets the souls of the fallen warriors in shape of a raven.