Celtic mythology took substance around 900BC, but there is little known during these times until 400BC where the Romano-Celts wrote inscriptions and writings of Christian monks. The Celts were not literate so many of the deities were never recorded. Celtic Beliefs were dominant until about 500AD when many of the people were turned to Christianity. There is still practice of Celtic beliefs today in modern culture, and many christen celebrations are on Celtic feasts or celebrations.