Videssos empire. Lost Legion series

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 of 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, tribune Marcus Scaurus was bored. The legion that had been magically transported to this strange world was far away. But the Emperor's niece Alypia was near -- and willing.
When their secret trysts were betrayed, Emperor Thorisin Gavras was forced to condemn Marcus as a traitor -- but with a promise of freedom and Alypia, if he could reclaim a rebel province from a fanatic usurper, with no military aid. With only centurion