Freedom of Religion/History/Source
What is the oldest source in any country that mentions this right?
The Edict of Toleration by Galerius in April of 311 ended Christian persecutions and granted their right to exist (Keresztes, "From the Great Persecution to the Peace of Galerius," 390). This preceded the Edict of Milan by two years, which permanently declared religious toleration and protection for Christians within the Roman Empire (Britannica, "Edict of Milan").