Why Nero?
In this, Nero was a ruthless, ultra-competent warrior. In the real world, Nero did things like ban the slaying of gladiators. He was known for focusing on cultural matters over martial needs. He was renowned for his use of poison to assassinate his enemies and committed suicide. See http://en.wikipedia.org/wiki/Nero for more info.
So I ask, why Nero? Why not some earlier Roman? Julius? Mark Antony? Or someone like Alexander the Great? Someone who might reasonably be expected to have the martial accomplishments credited to the Nero character in this movie.