Sasanian civil war of 589–591

In 588, a massive Hephthalite-Turkic army invaded the Sasanian province Harev. Bahram Chobin, a military genius from the House of Mihran, was appointed as the spahbed of the kust of Khorasan. He was thereafter appointed as the head of an army of 12,000 soldiers. He then made a counter-attack against the Turks, and successfully defeated them, killing their ruler Bagha Qaghan (known as Shawa/Sava/Saba in Sasanian sources).[2] After some time, Bahram was defeated by the Byzantine Empire in a battle on the banks of the Aras River. Hormizd IV, who was jealous of Bahram Chobin, used this defeat as an excuse to dismiss Bahram Chobin from his office, and had him humiliated.[5][2]

Bahram, infuriated by Hormizd's actions, responded by rebelling, and due to his noble status and great military knowledge, was joined by his soldiers and many others. He then appointed a new governor for Khorasan, and afterwards set for Ctesiphon.[6] This marked the first time in Sasanian history that a Parthian dynast challenged the legitimacy of the Sasanian family by rebelling.[7] Azen Gushnasp was sent to suppress the rebellion, but was murdered in Hamadan by one of his own men, Zadespras. Another force under Sarames the Elder was also sent to stop Bahram, who defeated him and had him trampled to death by elephants.[8] The route taken by Bahram was presumably the northern edge of the Iranian plateau, where he repelled a Roman-funded attack by Iberians and others on Adurbadagan, and suffered a minor setback by a Roman force employed in Transcaucasia.[9] He then marched southwards to Media, where Sasanian monarchs, including Hormizd, ordinarily resided during summer.[9]

Coin of Khosrow II, minted in 590.

Hormizd then left for the Great Zab in order to cut transmissions between Ctesiphon and the Iranian soldiers on the Roman border.[9] Around that time the soldiers were situated outside Nisibis, the chief Iranian city in northern Mesopotamia; they however also rebelled against Hormizd and pledged their allegiance to Bahram.[9] The influence and popularity of Bahram continued to grow increasingly; Sasanian loyalist forces sent north against the Iranian rebels at Nisibis were flooded with rebel propaganda.[9] The loyalist forces eventually also rebelled and killed their commander, which made the position of Hormizd unsustainable, making him decide to navigate the Tigris river and take sanctuary in al-Hira, the capital of the Lakhmids.[9]

However, during Hormizd's stay at Ctesiphon, he was overthrown in a seemingly bloodless palace revolution by his brothers-in-law Vistahm and Vinduyih, "who equally hated Hormizd".[9][10] Hormizd was shortly blinded with a red-hot needle by the two brothers, who put Hormizd's oldest son Khosrow II (who was their nephew through his mother's side) on the throne.[11][9] The two brothers shortly had Hormizd killed with at least the implicit approval of Khosrow II.[9] Nevertheless, Bahram continued his march to Ctesiphon, now with the pretext of claiming to avenge Hormizd.[12]

Bahram Chobin fighting Sasanian loyalists near Ctesiphon.

Khosrow then took a carrot and stick attitude, and wrote the following to Bahram; "Khosrow, kings of kings, ruler over the ruling, lord of the peoples, prince of peace, salvation of men, among gods the good and eternally living man, among men the most esteemed god, the highly illustrious, the victor, the one who rises with the sun and who lends the night his eyesight, the one famed through his ancestors, the king who hates, the benefactor who engaged the Sasanians and saved the Iranians their kingship—to Bahram, the general of the Iranians, our friend.... We have also taken over the royal throne in a lawful manner and have upset no Iranian customs.... We have so firmly decide not to take off the diadem that we even expected to rule over other worlds, if this were possible.... If you wish your welfare, think about what is to be done."[13]

Bahram, however, ignored his warning, and a few days later he reached the Nahrawan Canal near Ctesiphon, where he fought Khosrow's men, who were heavily outnumbered but managed to hold Bahram's men back in several clashes. However, Khosrow's men eventually began losing their morale and were in the end defeated by Bahram Chobin's forces. Khosrow, together with his two uncles, his wives, and a retinue of 30 nobles, thereafter fled to Byzantine territory, while Ctesiphon fell to Bahram Chobin.[9]

Map of Sasanian Mesopotamia and its surroundings.

In order to get the attention of the Byzantine emperor Maurice (r. 582–602), Khosrow II went to Syria, and sent a message to the Sasanian occupied city of Martyropolis to stop their resistance against the Byzantines, but with no avail.[14] He then sent a message to Maurice, and requested his help to regain the Sasanian throne, which the Byzantine emperor agreed with; in return, the Byzantines would re-gain sovereignty over the cities of Amida, Carrhae, Dara and Martyropolis. Furthermore, Iran was required to stop intervening in the affairs of Iberia and Armenia, effectively ceding control of Lazica to the Byzantines.[15]

In 591, Khosrow moved to Constantia and prepared to invade Bahram Chobin's territories in Mesopotamia, while Vistahm and Vinduyih were raising an army in Azerbaijan under the observation of the Byzantine commander John Mystacon, who was also raising an army in Armenia. After some time, Khosrow, along with the Byzantine commander of the south, Comentiolus, invaded Mesopotamia. During this invasion, Nisibis and Martyropolis quickly defected to them,[9] and Bahram's commander Zatsparham was defeated and killed.[16] One of Bahram's other commanders, Bryzacius, was captured in Mosil and had his nose and ears cut off, and was thereafter sent to Khosrow, where he was killed.[17][18]

Some time later, Khosrow, feeling disrespected by Comentiolus, convinced Maurice to replace the latter with Narses as the commander of the south.[9][16] Khosrow and Narses then penetrated deeper into Bahram's territory, seizing Dara and then Mardin in February, where Khosrow was re-proclaimed king.[16] Shortly after this, Khosrow sent one of his Iranian supporters, Mahbodh, to capture Ctesiphon, which he managed to accomplish.[19]

Meanwhile, Khosrow's two uncles and John Mystacon conquered northern Azerbaijan and went further south in the region, where they defeated Bahram at Blarathon. Bahram then fled to the Turks of Ferghana.[20] However, Khosrow managed to deal with him by either having him assassinated or convincing the Turks to execute him.[20]