What event caused the emperor of Constantine to convert to Christianity?

The pivotal event that led Emperor Constantine to convert to Christianity was the vision he reportedly had before the Battle of Milvian Bridge in 312 AD. He saw a cross of light in the sky with the Words "In this sign, you will conquer." After winning the battle and attributing his victory to the Christian God, Constantine became a supporter of Christianity, ultimately leading to the Edict of Milan in 313 AD, which granted religious tolerance throughout the empire.