There are many examples in Irish stories and culture of both the old religion and the new co-existing. My mother was a devout Catholic. On May 1st every year she hung egg shells from a tree. Beltane, which means good fire, is the Celtic festival that welcomes back the warmth of the sun. The warming sun assured Celts that agriculture would be bountiful. The fertility of crops and cattle being important to subsistence farmers, as were the Celts.

The four-leaf clover legend is that if you find one, you will have luck; white clovers are considered to be even more lucky, due to their rarity. Historically it is believed that ancient Celts warded off evil with clovers.

The generation before me put four leafed clovers between the pages of their prayer books! The assimilation of Celtic mythology into Christianity is most apparent in Irish folklore.
In the myth, The Children of Lir, the swans are converted into their original human forms when they hear the ringing of a church bell for the first time.

Although I sometimes think that Patrick, and missionaries like him, destroyed a unique culture; the truth is that we would know very little about Celtic history unless Catholic monks recorded oral myths such as Tain Bu Culaigne. The "Tain" is known as the most complete Irish epic myth and recounts the tale of the cattle raid of Cooley.

This assimiliation by the Catholic missionaries is a double-edged sword really. The Celts were going to be assimilated into the Roman Empire, maybe those on the fringes of Europe might have survived, some in fact did; but the assimilation into the Christian faith meant destruction of the old ways, while recording the history of an oral tradition. An oral tradition was preserved due to religious invaders and their ability to keep a written record of events.

Left: The Celts

If you are interested in the Celts and their lives before Christianity arrived in Ireland, check out my book, "Mona The Body in the Bog."

Bottom image from http://www.fullissue.com/index.php/history-of-the-celts.html