"...another
birthday celebrated on the same date by the Romans of the
Empire, that of the unconquered Sun, who on December 25, the
winter solstice according to the Julian calendar, began
to rise to new vigour after his autumnal decline. ...The 'Dies Natalis Invicti' was probably
first celebrated in Rome by order of the Emperor Aurelian, an
ardent worshipper of the Syrian sun-god Baal."
- Christmas
in Ritaul and Tradition, Christian and Pagan, by Clement A. Miles, p.23
"In the calendar of
Canopus, 239 C.E., the notation 'Birthday of the Sun.
Light will increase' appears at the date of the solstice,
indicating some notion of the sun dying and being reborn
as a child."
- Toward the origins of Christmas,
by Susan K. Roll, p. 33