Phocas in the context of "East Roman army"

The Byzantine Empire under the Justinian dynasty began in 518 AD with the accession of Justin I. Under the Justinian dynasty, particularly the reign of Justinian I, the empire reached its greatest territorial extent since the fall of its Western counterpart, reincorporating North Africa, southern Illyria, southern Spain, and Italy into the empire. The Justinian dynasty ended in 602 with the deposition of Maurice and the accession of his successor, Phocas.

Heraclius (Greek: Ἡράκλειος, romanized: Hērákleios; c. 575 – 11 February 641) was Byzantine emperor from 610 to 641. His rise to power began in 608, when he and his father, Heraclius the Elder, the Exarch of Africa, led a revolt against the unpopular emperor Phocas.

Heraclius's reign was marked by several military campaigns. The year Heraclius came to power, the empire was threatened on multiple frontiers. Heraclius immediately took charge of the Byzantine–Sasanian War of 602–628. The first battles of the campaign ended in defeat for the Byzantines; the Persian army fought their way to the Bosphorus but Constantinople was protected by impenetrable walls and a strong navy, and Heraclius was able to avoid total defeat. Soon after, he initiated reforms to rebuild and strengthen the military. Heraclius drove the Persians out of Asia Minor and pushed deep into their territory, defeating them decisively in 627 at the Battle of Nineveh. The Persian Shah Khosrow II was overthrown and executed by his son Kavad II, who soon sued for a peace treaty, agreeing to withdraw from all occupied territory. This way peaceful relations were restored to the two deeply strained empires.

The Byzantine–Sasanian War of 602–628, also called the Last Great War of Antiquity, was fought between the Byzantine Empire and the Sasanian Empire. It was the final and most devastating conflict of the Roman–Persian wars (54 BC – AD 628). The previous war between the two powers had ended in 591 after the emperor Maurice helped the Sasanian king Khosrow II regain his throne. In 602, Maurice was murdered by his political rival Phocas. Khosrow declared war, ostensibly to avenge the death of the deposed emperor Maurice. This became a decades-long conflict, the longest war in the series, and was fought throughout the Middle East, the Aegean Sea, and before the walls of Constantinople itself.

From 602 to 622, the Sassanians gradually conquered much of the Levant, parts of Anatolia, and—for the first time—Egypt and several islands in the Aegean Sea. The counter-attacks of the new Byzantine emperor Heraclius from 622 to 626 eventually forced the Persians onto the defensive. Allied with the Avars and Slavs, the Persians attempted to take Constantinople in 626, but were defeated. In 627, allied with Turks, Heraclius invaded the heartland of Persia. After the Battle of Nineveh (627), Iranian forces were finally broken, forcing civil war-torn Persia to seek peace.

Heraclius the Elder (Greek: Ἡράκλειος, romanized: Hērákleios; died 610) was a Byzantine Roman general and the father of Byzantine Roman emperor Heraclius (r. 610–641). Heraclius the Elder distinguished himself in the war against the Sassanid Persians in the 580s. As a subordinate general (or hypostrategos), Heraclius served under the command of Philippicus during the Battle of Solachon and possibly served under Comentiolus during the Battle of Sisarbanon. Circa 595, Heraclius the Elder is mentioned as a magister militum per Armeniam sent by Emperor Maurice (r. 582–602) to quell an Armenian rebellion led by Samuel Vahewuni and Atat Khorkhoruni. Around 600, he was made the exarch of Africa and in 608, he rebelled with his son against the usurper Phocas (r. 602–610). Using North Africa as a base, the younger Heraclius managed to overthrow Phocas, beginning the Heraclian dynasty, which would rule Byzantium for a century. Heraclius the Elder died soon after receiving news of his son's accession to the Byzantine throne.

Theodosius (Ancient Greek: Θεοδόσιος, romanized: Theodósios; 4 August 583 – shortly after 27 November 602) was the eldest son of Roman emperor Maurice (r. 582–602) and was co-emperor from 590 until his deposition and execution during a military revolt. Along with his father-in-law Germanus, he was briefly proposed as successor to Maurice by the troops, but the army eventually favoured Phocas instead. Sent in an abortive mission to secure aid from Sassanid Persia by his father, Theodosius was said to have been captured and executed by Phocas's supporters a few days after Maurice. Nevertheless, rumours spread that he had survived the execution, and became popular to the extent that a man who purported to be Theodosius was entertained by the Persians as a pretext for launching a war against Byzantium. There is debate over whether this man was an imposter or genuinely Theodosius.