The Encyclopedia Britannica, volume-2 (1943-1973), under christmas says...

In the Roman world, the Saturnalia was a time of merrymaking and exchanging of gifts. Dec. 25th was also regarded as the birthdate of the Iranian mystery god, Mithra, the Sun of Righeousness. On the Roman New Year houses were decorathed with greenery and lights and gifts were given to children.

To these observances were added the German and Celtic Yule rites. Food and good fellowship, the Yule log and Yule cakes greenery and fir trees, gifts and greetings all commemorated different aspects of this festive season. Fires and lights, symbols of warmth and lasting life havealways been assciated with the winter festival, both Pagans and Christians