- Edict of Milan: Issued by Roman Emperors Constantine I and Licinius, it granted freedom of worship to all religions within the Roman Empire, effectively ending the persecution of Christians.
- Constantine's conversion to Christianity: Constantine I, who had previously been a follower of the sun god Sol Invictus, reportedly experienced a vision of a cross in the sky before the battle of Milvian Bridge, leading to his conversion to Christianity.
- Beginning of Constantine's reign as sole emperor: After defeating his rivals, Constantine became the sole ruler of the Roman Empire, marking a significant turning point in Roman history.