The Celts were tribes of people that inhabited Britain, Scotland, Ireland, and even Spain and France, in ancient times. Like many other tribes of warriors, they were known as barbarians by the Romans. They had long beards and long hair, they were very hairy. Romans tended to keep their hair short and their beards trimmed, so they thought the Celts looked uncivilized. The Celts also painted their skin blue, using paint made from a plant called Woad. Celts who painted themselves with Woad were sometimes called Woad Raiders. The Romans hated the Celts because some of them were known to practice human sacrifice. According to Roman sources, the druids, high ranking priests, were said to sacrifice men to the thunder god Taranis.
The Celts were pagans, not only worshipping gods of elements like lightning and water, but also worshipping gods of skills. For example, the god Lugh was the god of weapons who was good with spears and slings. The Celtic religion was called druidism, because of the druids. The druids were high priests who were very important in Celtic society and arranged for sacrifices, divination, and even played a part in the leadership of the village.
The main language spoken by the Celts was of course, Celtic.