Edict of Serdica

The Edict of Serdica, also called Edict of Toleration by Galerius, 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.
The Edict implicitly granted Christianity the status of "religio licita", a worship that was recognized and accepted by the Roman Empire. It was the first edict legalizing Christianity and preceded the Edict of Milan by two years.
History.
On February 23, 303, on the Terminalia feast, Emperor Diocletian, on the proposal of Galerius, issued a persecutory edict. The edict prescribed:
In 305, Diocletian abdicated and was replaced by Galerius, his successor, who continued persecution in the East until 311, when he granted Christians forgiveness, freedom of worship and (implicitly) the status of "religio licita".
Full text.
Promulgated in the name of the other official members of the Tetrarchy, the edict marked the end of persecutions against the Christians.