The proximity of the Saturnalia to the winter solstice leads to an exposition of solar monotheism, the belief that the Sun ("Sol Invictus") ultimately encompasses all divinities as one. Perceived relations among the Mithraic mysteries, the Dies Natalis Solis Invicti (the "Birthday of the Unconquered Sun") on December 25, and the Christian Nativity as celebrated in December are a matter of long-standing and complex scholarly debate.