Above; ''A Druid priestess bearing Mistletoe'', artist unknown.
Mistletoe
The ancient pre-Christian celebration of the Winter Solstice is one of the oldest winter celebrations in the world. The Winter Solstice falls on the shortest day of the year and has been celebrated in Britain from the earliest of times. The Druids would cut the mistletoe that grew on the oak tree and give it as a blessing. Oaks were seen as sacred and the winter fruit of the mistletoe was a symbol of life in the dark winter months. 
The Yule Log
It's believed that the Druids began the tradition of the Yule log. The Celts believed the sun stood still for twelve days in the middle of winter and during this time a log was lit to conquer the darkness, banish evil spirits and bring luck for the coming year.
Customs
These customs have been incorporated into both Christian and secular celebrations all over the world. Prior to the legalization of Christianity by the Emperor Constantine in 313, no universal date or celebration of the birth of Christ is recorded. Roman Pagans used to gather at the hill where the Vatican is now to commemorate the “Birth of the Unconquered Sun” This pagan feast was celebrated throughout the Empire either on December 25th, or January 6th, (depending on which calendar they were using). Most historians believe it was Constantine who replaced the pagan festival with that of Christmas. I find it somehow comforting to know that our ancestors celebrated the Winter Solstice and as times changed, belief changed, customs changed, the Solstice, under one name or another, has been constant through out history.
