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 reflects the historical account of Constantine's vision before the Battle of Milvian Bridge, where he reportedly saw a cross in the sky and interpreted it as a sign from the Christian God, which influenced his decision to convert to Christianity.