Belisarius I: Thunder at Dawn by Eric Flint, David Drake

Two complete novels in one volume—the beginning of the Belisarius saga.

An Oblique Approach: In northern India the Malwa have created an empire of unexampled evil. Guided or possessed by an intelligence from beyond time, with new weapons, old treachery, and an implacable will to power, the Malwa will sweep over the whole Earth. Only three things stand between the Malwa and their plan of eternal domination: the empire of Rome in the East, Byzantium; a crystal with vision; and a man named Belisarius, the greatest commander Earth has ever known.

In the Heart of Darkness: Having conquered sixth century India, the Malwa Empire is forging the subcontinent's vast population into an invincible weapon of tyranny. Belisarius, the finest general of his age, must save the world. Guided by visions from a future that may never be, he and a band of comrades penetrate the Malwa heartland, seeking the core of the enemy's power. And when Belisarius leads the forces of good, only a fool would side with evil.