The first emperor of this name ended the Tetrarchy, called the Council of Nicaea, and beat back Maxentius at the Battle of Milvian Bridge after seeing a cross in the sky.
The fifth emperor of this name got the epithet "the dung-named" for defecating during his baptism. An emperor of this name allegedly turned into marble and will be resurrected from his cave under the Golden Gate. That eleventh emperor of this name was the last Byzantine emperor. An emperor of this name apparently granted Pope Sylvester I all his territory in a faked (*) donation. The first emperor of this name ended the Tetrarchy, called the Council of Nicaea, and beat back Maxentius at the Battle of Milvian Bridge after seeing a cross in the sky. For 10 points, give this common name, shared by the first Christian Roman emperor.
The fifth emperor of this name got the epithet "the dung-named" for defecating during his baptism.
Constantine