The chief towns of Upper Moesia (and broader) were: Singidunum (Belgrade), Viminacium (now Old Kostolac), Remesiana (now Bela Palanka), Naissos (Niš), and Sirmium (now Sremska Mitrovica), the latter of which served as a Roman capital during the Tetrarchy. Seventeen Roman Emperors were born in the area of modern-day Serbia, second only to contemporary Italy. The most famous of these was Constantine the Great, the first Christian Emperor, who issued an edict ordering religious tolerance throughout the Empire.