Firelord Series by Parke Godwin

From the ruins of empire, a great king arises Enslaved for centuries, used and then abandoned by the Roman conquerors, Britain is a shattered land -- with petty warlords and tribal leaders fighting over its pieces like mongrel dogs. The time is ripe for a warrior-king who will unite this wounded realm -- and a young centurion courageously answers the call. name is Artorius Pendragon -- and it is his destiny conquer with indomitable iron... moreFrom the ruins of empire, a great king arises Enslaved for centuries, used and then abandoned by the Roman conquerors, Britain is a shattered land -- with petty warlords and tribal leaders fighting over its pieces like mongrel dogs. The time is ripe for a warrior-king who will unite this wounded realm -- and a young centurion courageously answers the call. name is Artorius Pendragon -- and it is his destiny conquer with indomitable iron. A man flawed, filth and painfully mortal -- a clear-eyed leader with a strong distaste for war's necessary cruelties -- he will know a glory unparalleled in historical annals...an ultimately, will lose his heart and his kingdom to greatest betrayal of all. less

King Arthur is dead. Surrounded by traitors and upstarts, Guinevere must defend the empire she struggled so desperately to help forge. But she is driven to the depths of servitude to a bold Saxon thane who is unaware of her true identity, and about to discover more of humanity than she ever imagined.

Journeying to a pagan world of old magic in order to spread his religious beliefs, Padree, a passionate young priest, encounters the extraordinary Dorelei, the leader of the mystical Faerie folk, who teaches him about the earth and spirituality. Reprint.