Ctesiphon
Sasanian period

By 226, Ctesiphon was in the hands of the Sasanian Empire, who also made it their capital and had laid an end to the Parthian dynasty of Iran. Ctesiphon was greatly enlarged and flourished during their rule, thus turning into a metropolis, which was known by in Arabic as al-Mada'in, and in Aramaic as Mahoze. The oldest inhabited places of Ctesiphon were on its eastern side, which in Islamic Arabic sources is called "the Old City" (مدينة العتيقة Madīnah al-'Atīqah), where the residence of the Sasanians, known as the White Palace (قصر الأبيض), was located. The southern side of Ctesiphon was known as Asbānbar or Aspānbar, which was known by its prominent halls, riches, games, stables, and baths. Taq Kasra was located in the latter.

The western side was known as Veh-Ardashir (meaning "the good city of Ardashir" in Middle Persian), known as Mahoza by the Jews, Kokhe by the Christians, and Behrasir by the Arabs. Veh-Ardashir was populated by many wealthy Jews, and was the seat of the church of the Nestorian patriarch. To the south of Veh-Ardashir was Valashabad. Ctesiphon had several other districts which were named Hanbu Shapur, Darzanidan, Veh Jondiu-Khosrow, Nawinabad and Kardakadh.

Severus Alexander advanced towards Ctesiphon in 233, but as corroborated by Herodian, his armies suffered a humiliating defeat against Ardashir I. In 283, emperor Carus sacked the city uncontested during a period of civil upheaval. In 295, emperor Galerius was defeated outside the city. That however, he returned a year later & won a victory which ended in the fifth and final capture of the city by the Romans in 299 is still speculative & according to Roman historian Udo Hartmann & several other scholars also "highly unlikely".

Hence that he returned it to the Persian king Narses in exchange for Armenia and western Mesopotamia is also likely to have never happened. In c. 325 and again in 410, the city, or the Greek colony directly across the river, was the site of church councils for the Church of the East.

After the conquest of Antioch in 541, Khosrow I built a new city near Ctesiphon for the inhabitants he captured. He called this new city Veh-Antiok-Xusrō, or literally, "better than Antioch Khosrow built this". Local inhabitants of the area called the new city Rumagan, meaning "town of the Romans" and Arabs called the city al-Rumiyya. Along with Weh Antiok, Khosrow built a number of fortified cities. After a campaign in 573, John of Ephesus wrote that no fewer than 292,000 persons had been deported from Dara, Apamia, and other Syrian towns to Veh-Antiokh. John would later cite a letter stating no more than 30,000 prisoners were deported. It's thought that the first number he gave is not to be taken literally.

In 590, a member of the House of Mihran, Bahram Chobin repelled the newly ascended Sasanian ruler Khosrow II from Iraq, and conquered the region. One year later, Khosrow II, with aid from the Byzantine Empire, reconquered his domains. During his reign, some of the great fame of al-Mada'in decreased, due to the popularity of Khosrow's new winter residence, Dastagerd. In 627, the Byzantine Emperor Heraclius surrounded the city, the capital of the Sassanid Empire, leaving it after the Persians accepted his peace terms. In 628, a deadly plague hit Ctesiphon, al-Mada'in and the rest of the western part of the Sasanian Empire, which even killed Khosrow's son and successor, Kavad II.

In 629, Ctesiphon was briefly under the control of Mihranid usurper Shahrbaraz, but the latter was shortly assassinated by the supporters of Khosrow II's daughter Borandukht. Ctesiphon then continued to be involved in constant fighting between two factions of the Sasanian Empire, the Pahlav (Parthian) faction under the House of Ispahbudhan and the Parsig (Persian) faction under Piruz Khosrow.
length_constraints:number_sentences[12], startend:quotation