Heraclius (ca. 575-641) was Byzantine emperor from 610 to 641. Ascending the throne when the empire seemed on the point of dissolution, he saved it from its immediate foes and gave it new institutional and cultural direction.

Born in Cappadocia, Heraclius was apparently of Armenian origins. His father, Heraclius, was a leading general under Emperor Maurice and became exarch (viceroy) of North Africa. When the regime of the usurper Phocas (602-610) degenerated into chaos, dissident elements in Constantinople urged the elder Heraclius to seize the throne; but the old exarch sent his son instead. The rebellion succeeded in overthrowing Phocas and enthroning Heraclius in October 610.

Because of Phocas's mismanagement, Heraclius faced a seemingly impossible situation. The Slavs and the Avars had overrun the Balkans and threatened anew the empire's remaining European territories. Meanwhile, the Sassanid king of Persia, Chosroes (or Khusru) II, began a war of conquest against the empire's eastern territories and soon detached Syria-Palestine (613-614) and Egypt (616). The Persians also menaced Asia Minor and the paths to the capital.

The empire's military and financial resources were inadequate to cope with these threats, and the ensuing years were spent in laborious preparations for defense. Precarious peace was purchased from the Avars, and in 622 Heraclius was ready to begin his counteroffensive. The Emperor assumed personal command of his troops and during the next 6 years campaigned vigorously.

The Avars and the Slavs mounted a fierce siege on Constantinople in 626; but the city resisted successfully, and Heraclius remained free to fight. His efforts gradually cleared Asia Minor, won the support of allies in the Caucasus, and even carried the war into Persian territory in Mesopotamia (627). Peace was settled with the weakened Persian government in 629. Having secured the eastern frontier, Heraclius made a triumphant return to Constantinople. Probably in 630, he solemnly restored to Jerusalem the True Cross and other Christian relics the Persians had carried off.

Heraclius attempted to restore the battered empire internally. With the promulgation of the Ékthesis (683) Heraclius unsuccessfully sought to end the religious strife among Christian factions. More far-reaching were the institutional changes of the period. Heraclius has been associated with the initiation of the Byzantine system of "themes," the military provinces organized around local native forces. This system would become the basis of the empire's strength for the next 4 centuries. Heraclius also defined the "Byzantine" character more clearly in terms of Greek language and culture.

Before Heraclius could complete his work of reconstruction, the Arabs, under the new banner of Islam, began assaults on the restored provinces. Possibly because of poor health, the Emperor failed to respond effectively. Worn out and disillusioned as much of his life's work crumbled, Heraclius died on Feb. 11, 641. He had, however, founded the dynasty that would direct the Byzantine Empire boldly and successfully through its most perilous period of transformation and survival.