The Edict of Milan, signed by Constantine the Great and co-emperor Valerius Licinius granting religious freedom throughout the Roman Empire, is posted in Nicomedia.
The Edict of Milan (Latin: Edictum Mediolanense, Greek: Διάταγμα τῶν Μεδιολάνων, Diatagma tōn Mediolanōn) was the February 313 AD agreement to treat Christians benevolently within the Roman Empire. Western Roman Emperor Constantine I and Emperor Licinius, who controlled the Balkans, met in Mediolanum (modern-day Milan) and, among other things, agreed to change policies towards Christians following the edict of toleration issued by Emperor Galerius two years earlier in Serdica. The Edict of Milan gave Christianity legal status and a reprieve from persecution but did not make it the state church of the Roman Empire. That occurred in AD 380 with the Edict of Thessalonica.
The document is found in Lactantius's De mortibus persecutorum and in Eusebius of Caesarea's History of the Church with marked divergences between the two. Whether or not there was a formal 'Edict of Milan' is no longer really debated among scholars who generally reject the story as it has come down in church history.The version found in Lactantius is not in the form of an edict. It is a letter from Licinius to the governors of the provinces in the Eastern Empire he had just conquered by defeating Maximinus later in the same year and issued in Nicomedia.