This is a completely new scenario for Rome II, set in 311 A.D. Also available on Steam Workshop. The Tetrarchy of Diocletian Augustus divided the Empire in 293 A.D. Not long after, tensions arose between the various Emperors, all vying to become sole sovereign of the Roman world.
Is that a decapitation I can see? If so, how did you get it?
The official Blood & Gore DLC, unrelated to the mod.