Heraclius took the throne of a dying empire. Persia had overrun its eastern provinces, and the capital itself would soon come under siege; the situation looked hopeless. Then, in one of history's great reversals, Heraclius led a daring counter-offensive deep into Persian territory and broke the enemy at Nineveh. He saved the Roman East, only to face, in his last years, a new and seemingly unstoppable power rising from Arabia.
An empire on the brink
When Heraclius seized power in 610, overthrowing the tyrant Phocas1, the empire was collapsing. The Sasanid Persians under Khosrow II had taken Syria, Palestine and Egypt, carried off the relic of the True Cross from Jerusalem2, and in 626 their allies the Avars besieged2 Constantinople itself. The city held behind its walls, but the empire had lost its richest lands.
The great counter-offensive
Rather than defend, Heraclius gambled. From 622 he led his reorganised army by bold marches3 into the heart of the Persian Empire, campaigning year after year far from home. In 627, near the ruins of ancient Nineveh, he brought the Persians to battle and shattered their army4. Khosrow was overthrown, Persia sued for peace3, and the lost provinces and the True Cross were returned.
The Arab conquests
Heraclius had barely restored the East when a new force appeared. In the 630s the armies of the young Islamic caliphate swept out of Arabia. At the Battle of Yarmouk in 636 the exhausted Byzantine army was destroyed2, and within a few years the provinces Heraclius had just won back were lost for good, Syria and Palestine in his lifetime and Egypt in the years around his death. He was too old and ill to take the field himself against them.
The measure of the man
Heraclius died in 641, his last years shadowed by defeat2. Yet his achievement was immense: he had saved the empire when it seemed doomed, and reshaped it for the long struggle ahead, even elevating Greek, already the common tongue of the East2, as the language of his government. His reign is the hinge between the late Roman world and the medieval Byzantine one.
See the disaster that undid his gains at Yarmouk, or meet the other great commanders of the Byzantine Empire.