Phocas was Byzantine emperor from 602 to 610. Initially a middle-ranking officer in the Eastern Roman army, Phocas rose to prominence as a spokesman for dissatisfied soldiers in their disputes with the court of the Emperor Maurice. When the army revolted in 602, Phocas emerged as the natural leader of the mutiny. The revolt proved to be successful and led to the capture of Constantinople and the overthrow of Maurice on 23 November 602 with Phocas declaring himself emperor on the same day.

The Eastern Roman army refers to the army of the eastern section of the Roman Empire, from the empire's definitive split in 395 AD to the army's reorganization by themes after the permanent loss of Syria, Palestine and Egypt to the Arabs in the 7th century during the Byzantine-Arab Wars. The East Roman army was the continuation of the Late Roman army of the 4th century, until it gradually transformed into what is now called the Byzantine army from the 7th century onwards.