Theodosius' Persian War

Location
 Roman EmpireChristian ArmeniansAdiabeneArab allies
  Theodosius
Vardan Mamikonian
Marcian
Acacius
Proculus
Romulus
Tuscianus
Procopius
Ghevond Vanandetsi
Abbousta
Sixtus
Mushkan Niusalavurt
Mihr Narseh
Izad Gushnasp
Ashtat
Vasak of Syunik

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Theodosius prepared his armies at Ninive for an invasion of the Sasanian Empire. Firstly Theodosius sent his trusted friend Acacius with a small force to aid the Armenians, along with him went Marcian’s young brother Romulus(serving as a tribune). Tuscianus, another close friend and ally, was made Dux Mesopotamiae, to govern Mesopotamia and Babylonia in Theodosius’ stead while he was fighting in Persia. Theodosius himself, along with Marcian, Proculus, and a few other generals) gathered the main army.

Upon receiving reports of the gathering Roman forces the massive Persian army under Steven abandoned its March north to Armenia and turned to meet Theodosius’ growing forces. Theodosius, always one to take the initiative, began is invasion, possibly prematurely, and the two armies both moved into the Persian province of Adiabene, which boasted a Christian majority. The Adiabene bishop Abbousta raised a small force of local Christians to aid Theodosius, and provided the Romans with a network of scouts and spies across the region. On 10 June 1204 the two armies met on the plain between Arbela and the Great Zab River, and, at the Battle of Arbela, Theodosius won decisively.

What remained of the Sassanid army fled over the mountains into Atropatene. After the surrender of Arbela Theodosius split his army in two. Marcian took one half through Adiabene executing a pincer movement with the allied Roman-Armenian army under Acacius and Varda that trapped the remnants of the Sassanid army in Atropatene. This succeeded and left some 50,000 Persians besieged in Ganzak.

Meanwhile Theodosius took the other half of his army south into Babylonia, meeting up with troops marshaled by Tuscianus, and invaded Susiana, capturing Susa on 4 September 1204. Following in the footsteps of Alexander, after taking Susa Theodosius crossed through the Zagros at the Persian Gates into the Persian heartland. The Sassanid capital, Istakhr, fell on 1 March 1205 after a brutal six month siege. With Persia at his feet Theodosius spent the next few months looting cities and establishing client kingdoms throughout western Persia. During this period he met the Persian noblewoman Kurdiyah, who is said to have fallen in love with. They married on 13 April 1205.

After capturing the city of Yazd, Theodosius began to consider whether to end his Persian adventure. According to the historian Hydatius, Theodosius' two closest friends both petitioned Theodosius, one to turn west and the other east. Tuscianus begged Theodosius to turn back and return to take control of Rome. Whereas Acacius, ever the easterner, spoke that Theodosius could fashion himself the next Alexander, and carve out a new empire in the east. Theodosius seems to have considered this question for some time. Some, not very historical, sources say he was visited again by Angels that convinced him to return and liberate Rome from pagans. Reluctantly, Theodosius decided to return west. He signed the Peace of Yazd with the Sassanids on 3 January 1206, installing the Christian Sassanid Caoses or Kavus on the Persian throne, and began the march back to Babylonia.