Simplify the following text for a Grade 11 native English-speaking person.
Original: However , it became an officially supported religion in the Roman state under Diocletian 's successor , Constantine I , with the signing of the Edict of Milan in 313 , and quickly became dominant .
Simplified: However , Christianity became an officially supported religion in the Roman Empire under Constantine I , who was the next Emperor . With the signing of the Edict of Milan in 313 , it quickly became the biggest religion .