The campaign of A.D. 589 was opened by a brilliant stroke on the part of the Persians, who, through the treachery of a certain Sittas, a petty officer in the Roman army, made themselves masters of Martyropolis.  It was in vain that Philippicus twice besieged the place; he was unable to make any impression upon it, and after a time desisted from the attempt.  On the second occasion the garrison was strongly reinforced by the Persians under Mebodos and Aphraates, who, after defeating Philippicus in a pitched battle, threw a large body of troops into the town.  Philippicus was upon this deprived of his office, and replaced by Comentiolus, with Heraclius as second in command.  The new leaders, instead of engaging in the tedious work of a siege, determined on re-establishing the Roman prestige by a bold counter-attack.  They invaded the Persian territory in force, ravaged the country about Nisibis, and brought Aphraates to a pitched battle at Sisarbanon, near that city.  Victory seemed at first to incline to the Persians; Comentiolus was defeated and fled; but Horaclius restored the battle, and ended by defeating the whole Persian army, and driving it from the field, with the loss of its commander, who was slain in the thick of the fight.  The next day the Persian camp was taken, and a rich booty fell into the hands of the conquerors, besides a number of standards.  The remnant of the defeated army found a refuge within the walls of Nisibis.  Later in the year Comentiolus recovered to some extent his tarnished laurels by the siege and capture of Arbas, whose strong situation in the immediate vicinity of Martyropolis rendered the position of the Persian garrison in that city insecure, if not absolutely untenable.

Such was the condition of affairs in the western provinces of the Persian Empire, when a sudden danger arose in the east, which had strange and most important consequences.  According to the Oriental writers, Hormisdas had from a just monarch gradually become a tyrant; under the plea of protecting the poor had grievously oppressed the rich; through jealousy or fear had put to death no fewer than thirteen thousand of the upper classes, and had thus completely alienated all the more powerful part of the nation.  Aware of his unpopularity, the surrounding tribes and peoples commenced a series of aggressions, plundered the frontier provinces, defeated the detachments sent against them under commanders who were disaffected, and everywhere brought the empire into the greatest danger.  The Arabs crossed the Euphrates and spread themselves over Mesopotamia; the Khazars invaded Armenia and Azerbijan; rumor said that the Greek emperor had taken the field and was advancing on the side of Syria, at the head of 80,000 men; above all, it was quite certain that the Great Khan of the Turks had put his hordes in motion, had passed the Oxus with a countless host, occupied Balkh and Herat, and was threatening to penetrate into the very heart of Persia.  The