When Constantinople Was Besieged by The Persians | How did it Happen?

TL;DR

In 626 AD, Constantinople survived a coordinated Avar-Persian siege because the Roman navy destroyed Slavic amphibious assaults and the Theodosian walls held every land attack.

Key Points

• 1.Decades of Roman weakness made the siege inevitable. After Maurice's murder by the usurper Phocas in 602 AD, civil wars crippled the eastern frontier, allowing Persia to conquer Mesopotamia, Armenia, the Caucasus, the Levant, and Egypt between 602–619 AD.
• 2.Emperor Heraclius rebuilt Roman power before the siege. Starting in 622 AD, he reorganized the imperial army and transferred Balkan troops eastward, stabilizing the Anatolian frontier and winning several victories against the Persians.
• 3.The 626 siege was a dual-front assault on the capital. An Avar-Slavic army of up to 80,000 attacked Constantinople's land walls while Persian general Shahbaraz camped across the Bosporus at Chalcedon, ready to send reinforcements.
• 4.Constantinople's defenses and Roman sea power defeated every assault. The layered Theodosian walls repelled repeated land attacks; the Roman navy crushed two Slavic amphibious attempts on the Golden Horn and intercepted Persian troops crossing the strait.
• 5.The siege's failure reversed the entire war's momentum. Heraclius exploited Persian general Shahbaraz's defection after intercepting Khosrow's execution order, allied with the Turks, defeated Persia at Nineveh in 627 AD, and captured the royal palace at Dastagerd, recovering 300 military standards.
• 6.The war ended with Rome restored but both empires fatally weakened. Khosrow II was deposed and executed in 628 AD; a peace treaty returned all Roman territory and the True Cross to Constantinople — but depleted Roman and Persian militaries left both empires exposed to the rising Arab armies from the Arabian Peninsula.