The Celts transmitted their culture orally, never writing down history or facts. This accounts for the extreme lack of knowledge about them prior to their contact with the classical civilizations of Greece and Rome. They were generally well educated, particularly on topics such as religion, philosophy, geography and astronomy. The Romans often employed Celtic tutors for their sons, many of these tutors were Druid priests. Religion was a force in Celtic culture. The Druids were their priestly caste. The Celts were extremely superstitious.  
The history of the Celtic peoples goes back some thousands of years . At one time all of Europe was Celtic. England was ruled entirely by Celts . Eventually the Romans, Angles and Saxons came and pushed the Celts to the north and west. One of the great Celtic events of history was the Fifth-Century battle between King Arthur and his Celtic army against the dark pagan hordes in England ( as the Celts termed the non-Celtic peoples ). The Celts considered King Arthurs loss to be the death of civilization. King Arthur himself remains an important figure in Celtic legend. The original historic story is now much embroidered with medieval knights and traditions.

The ancient Celtic Art was full of interlacing patterns, elaborate knotwork, spirals, animal forms and animal zoomorphics, and color. The early Celts displayed their art especially in metal: jewelry , weapons (they were fierce warriors ), figurines and pots are some of the many artifacts that come to light.
Knotwork tradition in manuscript painting spread the style from Britain and Ireland to Scotland (in those days Pictland and Dalriada), Wales and Northumbria and with the travels of missionaries of the Celtic church to Europe. Viking raiders later appropriated many of the design concepts into their own personalized , more chaotic style of animal interlace.  
When Christianity came to the Celtic lands of Britain and Ireland, the monks of the seventh century adapted the ancient Celtic art forms to the new religion. The Celtic cross and the Tree of Life,and the written form of the Celtic horoscope, for example came from this marriage. Writing also came to the Celts for the first time. The most famous manuscript by the monks is the beautiful Book of  Kells, on display in the library of Trinity College in Dublin.