Eagle and Empire (The Hesperian Trilogy #3) by Alan Smale
The award-winning author of Clash of Eagles and Eagle in Exile concludes his masterly alternate-history saga of the Roman invasion of North America in this stunning novel. Praetor Gaius Marcellinus came to North America as a conqueror, but after meeting with defeat at the hands of the city-state of Cahokia, he has had to forge a new destiny in this strange land. A decade since his arrival, an unstable peace exists between the invading Romans and a loose affiliation of Native American tribes known as the League. But invaders from the west threaten that peace, plunging the continent into war: The Mongol Horde has arrived.Marcellinus and his Cahokian friends must summon allies both great and small in preparation for a final showdown. Alliances will shift and foes will rise as the dramatic final battle for the future of the continent comes ever closer.