The "Oxford Companion to Christian Thought" also remarks on the uncertainty about the order of precedence between the celebrations of the Birthday of the Unconquered Sun and the birthday of Jesus: "This 'calculations' hypothesis potentially establishes 25 December as a Christian festival before Aurelian's decree, which, when promulgated, might have provided for the Christian feast both opportunity and challenge." Susan K. Roll calls "most extreme" the unproven hypothesis that "would call Christmas point-blank a 'christianization' of Natalis Solis Invicti, a direct conscious appropriation of the pre-Christian feast, arbitrarily placed on the same calendar date, assimilating and adapting some of its cosmic symbolism and abruptly usurping any lingering habitual loyalty that newly-converted Christians might feel to the feasts of the state gods".