Why is Christmas in December instead of April?
Because Pope Julius I declared that the birth of Christ was to be celebrated on December 25 in about 350 CE. But mainly because the early Christian church found it politically convenient to place the date during a time when older, Pagan religions celebrated various holidays like the Saturnalia, the birth of Mithras, the natalis solis invictus (birth of the unconquered sun, i.e. the winter solstice), etc.
