Source 2: http://www.druidsgrove.com

Other classes in the old Celtic social order: the warrior-aristocracy; out-caste Fianna warriors; (see Warriors) Bards, brehons (lawyers), historians and other more specialized professionals; land-holders (landlords); freeborn laborers; and non-freeborn laborers. Celtic law included ways for anyone, including non-freeborn laborers, to move up or down the social hierarchy; what rights and responsibilities were due to each of them, and what kind of punishment could be given to criminals according to their status (for more was expected from those who had more). An old Celtic proverb goes: "A man is better than his birth". 

Bards and Fili were the primary keepers of the histories, genealogies, laws, poetry, music and stories of the Celtic people. Their training was similar to the Druid's training, and their rank in society was second only to the King. A bard was expected to be able to perform what were called the "three noble strains", which were music to inspire laughter, tears, or sleep. They were guaranteed to receive special hospitality wherever they went, and be free from insult, among other rights; a breach of this would allow the bard to compose a satire-poem that would tarnish the offender's reputation for generations to come.

The Celtic noble class held the political and economic power of the tribe. Kingship was passed from king to his son, or (as in the case of the Picts) from king to mother's son. Many Celtic tribes actually elected their king for a lifelong term, from among eligible men whose ancestors were kings. Of interest to those who study Druidism is the concept of the sacred king, in which the king was ritually married to the Goddess of the land. Sometimes a Druidess (or, as in one recorded case from Donegal, Ireland, a horse) would temporarily represent the Goddess to whom the king was married. He had to rule justly and honorably in order to satisfy his immortal spouse, for if he did not the land would become barren and infertile, and the tribe's prosperity would decline, an event which occurs reasonably frequently in mythology. The king had to be in full health and without physical blemish as well to please her, and this is why the god Nuada had to abdicate the throne when he lost his hand in battle. A sacred king would also be bound by a geas, (see Geas) as an additional condition for his prosperous rule. This ritual is evidence for a Druidic doctrine of the unity of humans and nature.