Videssos Besieged (Time of Troubles/Harry Turtledove, Bk 4)

With the arrival of spring, the Emperor Maniakes vows to unleash his troops against the enemy capital, where a hated despot sits arrogantly upon the throne. But from the moment Maniakes reaches the land of the Thousand Cities, he is plagued by a question no one can answer. Where is his nemesis, the ruthless commander whose cavalry no opposing force can withstand?.