The comparison of Christ with the astronomical Sun is common in ancient Christian writings. In the 5th century, Pope Leo I (the Great) spoke in several sermons on the Feast of the Nativity of how the celebration of Christ's birth coincided with increase of the Sun's position in the sky. An example is: "But this Nativity which is to be adored in heaven and on earth is suggested to us by no day more than this when, with the early light still shedding its rays on nature, there is borne in upon our senses the brightness of this wondrous mystery.