Answer
On June 25, 610 A.D., Phocas, the emperor of the Byzantine Empire, was executed and Heraclius declared himself Emperor. Phocas had seized the throne in 602 A.D. by assassinating the previous emperor, Maurice. Heraclius, who was the nephew of Maurice, had been leading an army against the Persians when he learned of Phocas's coup. Heraclius returned to Constantinople and quickly defeated Phocas's forces.