Yule Log
The Yule Log most likely began as part of pagan ritual related to the Winter Solstice. It was felt that burning a log would keep evil spirits away, over the extended period of darkness.
As Christianity became more commonly adopted, it simply became associated with the Christmas celebration. Traditionally men would go out into the forest to find the perfect log for the occasion.
Adapted from: Christmas: Its Origin and Associations by W.F. Dawson