Rome and the Sasanians

Romantasy and Alternative History novel set in an alternative 4th century Roman Empire   Rome is powerful and prosperous. After a short succession crisis in the middle of the 3rd century, the arrival on the throne of a new powerful dynasty has restored the pax romana. The invention of a new type of forest-based magic has even allowed its latest emperor to manage a conquest that had long eluded Rome: Magna Germania.   However, Rome is not the only one to have thrived. The Persians are back, and with a new kind of terrifying magic manipulating fire itself! The new Persian Sasanian dynasty has annihilated the old enemies of Rome, the Parthians and the latest Sasanian king has brought his conquest to the Roman Empire itself, first by taking Anatolia, then Achaea. His eyes are now set on Dalmatia...   It is such a Sasanian incursion into that region that forces the Roman emperor's estranged wife and daughter to come back to Rome. There, Livia, the daughter in question, is thrust at the centre of her parent's quarrels, the deadly politics of the imperial court, and the attention of the Sasanian king...