An Emperor for the Legion — Harry Turtledove

SWORDS AGAINST SORCERY

Foul sorcery had slain the Emperor. Now the army of Videssos, betrayed by one man's craven folly, fled in panic from the savage victors. But there was no panic in the Legion, mysteriously displaced from Gaul and Rome into this strange world pf magic.

Wearily, Tribune Marcus Scaurus led his men through the chaos and enemy hordes in search of winter quarters, to regroup and seek to join up with Thorisin Gavras, now rightful ruler of Videssos.

But in Videssos the city, capital of the beleaguered realm, Ortaias Sphtntzes, whose cowardice had caused their defeat, now sat upon the throne. There, behind great walls that had always made the city impregnable to storm or siege, he ruled with the support of evil sorcery. Overthrowing him seemed impossible.

Grimly, Marcus Scaurus began the long march through hostile country toward that seemingly hopeless attempt.