One leader whose single-day decision altered centuries of history was Constantine the Great at the Battle of the Milvian Bridge in 312 CE. On the morning of the battle, Constantine reportedly saw a vision of the Christian cross in the sky with the words “In this sign, conquer.” He ordered his soldiers to mark their shields with the Christian symbol, and after winning the battle, he embraced Christianity, later issuing the Edict of Milan in 313 CE granting religious tolerance across the Roman Emp