From the publisher (HinterWelt Enterprises):
Roma Imperious is where Alternate History meets Roman Fantasy. During the rule of Constantine, pressed to defeat Maxentius at the battle of the Milvian Bridge, he turns to a group of ambitious druids. They perform a ritual, calling on their gods to give victory to Constantine. In exchange for the spell, Constantine promises freedom for the peoples of western Europe. He would not keep that promise and further he would demand their secrets. The Druids, over the next four hundred years, would rise against Roma demanding their due.
Meanwhile, Rome would follow its own path, building and researching magic in their own way. As the world changes, magic becomes more common and the barbarians flounder in ancient rituals the Romans would push forward into newer and more reliable forms of magic.