Origin
The origin of the Celts has proven troublesome to ascertain. Although descendants of the Celts today are found mainly on the British Isles, as well as Ireland, the Celts themselves probably originated in mainland Europe. To define them to a strict location is impossible, but they left evidence along the Alpine mountain range; encompassing what is today Austria, Germany, Switzerland, France, Czechia, Slovakia and Hungary. Since they had no written language, and the fact that they were driven out by invasions and famine, the Celts would trace their origins to central Europe, with smaller settlements found as far as North Africa, the Middle East and the Caucasus.
Settlements
Roman records, as well as archeological evidence, show us that the Celts had impressive fortifications and settlement placements. They would build their towns on higher altitudes on the mountains and ridges, yet never expose them to be seen from afar, always built surrounded by forests. Foraging and hunting were the main reasons as to why they would prefer this, as well as being able to easily lose an enemy if they were tracked. Since they preferred to be high on the mountains and nested deeply into the forests, their fortifications were nearly impossible to breach.
Roads
The Romans are usually credited to be the pioneers in terms of road construction; yet it’s less known that they built upon foundations laid by the Celts. Indeed, the Celts would seem to be the first to place well-laid roads, as huge planks and logs of wood were the preferred building materials. The only lackluster aspect of their roads was the fact that only they knew where they were. Little to no maps to where their roads led are left; plus the fact that over brief periods of time, the wood would degrade due to the weather they were exposed to.
Wealth
Contrary to the belief that the Celts were lacking wealth, is the abundance of copper, silver, gold and minerals found in their archeological sites. Being organized, as well as having little to no opposition, would confirm how they were able to obtain their riches. Mining was common among the Celts; as well as preying upon travelers or caravans on their roads. Warring with the Germanic tribes, pillaging, raiding and piracy in the Mediterranean confirm this, as well. Greek historians note that free companies and settlers of Celts were common all around the Old World.
Language
Although never developing writing, nor leaving any records apart from their oral traditions, the language of the Celts is found even today among their descendants. Surviving various invasions, ranging from the Greeks, to the Romans, to the Huns and what else, their language adapted, and evolved. Merging with their invaders, in a way their language intertwined and evolved, sparing it from destruction. The aggressive expansion of the Romans, driving the Celts from their land, had also helped. The most pure in form is found today in Scotland and Ireland, as these places had very little to no factors to influence it.
Tools and weapons
An interesting note for the Celts is their usage of bronze and iron. Over the years, it would seem that the Celts had perfected the production of quality tools and weapons. Bronze and iron being found in mines on mountain ranges where the Celts settled, would confirm this as well. Archeological evidence and records of Greeks and Romans confirm the craftmanship of the Celts. Their tools and weapons being made out of bronze and iron, the Celts still preferred wood for constructing roads and settlements. The intertwined and beautifully-carved wood they left behind, and the skills passed down the generations, hardly make the Celts savages.
War
When it came to the inevitable, the Celts held their ground, even expanded widely through war. Pushing back the Germanic tribes, invading the Balkans, and being resistant to Roman rule proves this claim. The biggest rivals to the Roman Republic were the various Celtic tribes. Raiding them, pillaging and causing all sorts of troubles for them at first, and later resisting them to the bitter end. Employing light troops, preferring ambushes and quick attacks, the Celts used guerilla tactics, preferring it to the traditional warfare of the time.
Equality
Something not often seen in history is equality between the two sexes. Yet the Celts considered women to be equal to their male counterparts. Letting them have jobs, choosing who they would marry and divorce, allowing them to accumulate power if they would prove themselves, many were the liberties of Celtic women. Because of that, it was no surprise that the elder of a village or town was usually a woman. Chieftains and queens, even being druidesses, women in Celtic society enjoyed various freedoms to prove themselves to their kinsmen.
Druidism
One of the oldest religions, and a belief of higher beings, is druidism, created by the Celts. Their connection to nature, and everything related to naturality was the core of druidism. As the Celts viewed the elements of nature divine, it comes as no surprise the veneration of said elements as gods. The druid or druidesses of a clan were the highest positions obtainable. They were the ones teaching the younger generations and their kinsmen how to live life according to their beliefs. Creating and passing traditions, intertwining with the everyday life of the Celts is how druidism survived and left traces still seen today in various forms.
Sacrifice and headhunting
Sacrificing was staple to the druidic beliefs of the Celts. Requiring numerous ways to please the demands of their gods, the Celts would build altars dedicated for that sole purpose. Sacrificing food, medicinal herbs, animals, and even humans, the Celts had a plethora of options. The most common one was the day-to-day capability of sacrificing what is not needed by the clan. Food and animals being the staple, humans would be sacrificed on specific dates, be they kin or enemy alike. A human head became the greatest treasure a Celt could possess. The obsession to accumulate as many skulls as one was capable of, came from the belief that the skulls held the souls of their victims. Pride and accomplishment to be the one with the most skulls came hand in hand in Celt society. Their enemies viewed it as barbaric as one could be capable of, fear spreading and bone chilling to how low the Celts could stoop.