The Edict of Serdica, also called Edict of Toleration by Galerius,[1][2][3] was issued in 311 in Serdica (now Sofia, Bulgaria) by Roman Emperor Galerius. It officially ended the Diocletianic Persecution of Christianity in the Eastern Roman Empire.[4]

The Edict implicitly granted Christianity the status of religio licita, a worship that was recognized and accepted by the Roman Empire.[5] It was the first edict legalizing Christianity and preceded the Edict of Milan by two years.

Edict of Serdica – Wikipedia

https://en.wikipedia.org/wiki/Edict_of_Serdica

The Edict of Serdica, also called Edict of Toleration by Galerius,[1][2][3] was issued in 311 in Serdica (now Sofia, Bulgaria) by Roman Emperor Galerius. It officially ended the Diocletianic Persecution of Christianity in the Eastern Roman Empire.[4]