The statement that best evaluates why Constantine I converted to Christianity during his fight to gain control of the Roman Empire is:
Constantine thought he saw a cross in the sky the night before a big battle and believed this celestial clue helped him win the battle.
This event, which is often referred to as the vision of the cross or the "Chi-Rho" vision, is a significant moment in Constantine's story and is commonly cited as a turning point that influenced his conversion to Christianity and subsequent actions to favor the religion within the Roman Empire.