The reference in the Kartēr inscription to two sects of Christians continues the indications from Syriac sources that Christianity had by that time (the second half of the 3rd century) gained a firm footing in the lands of the Tigris and the Euphrates, where it was strongest among the Aramaic-speaking communities. Ultimately, Christian missionary effort came to expand over the whole of Iran and even beyond. As long as the Roman Empire remained pagan, the Christian communities of Iran lived undisturbed by persecution, while the Christians themselves showed outspoken hostility toward such heterodox sects as the Manichaeans and the Gnostic followers of Marcion (the Marcionites) and Bardesanes, who existed side by side with them. Once the emperor Constantine I (the Great; reigned 306–337) made Christianity the official religion of the Roman world, the Iranian Christians were drawn to feel a certain sympathy for their foreign coreligionists, and political significance came to be attached by the Sāsānian rulers to these religious connections with an often hostile foreign power. After 339 the Christians of Iran were subjected to severe persecutions at the hands of Shāpūr II and his successors. Nonetheless, substantial Christian communities survived in parts of Iran long after the end of the Sāsānian dynasty. Manichaeism
During the reign of Shāpūr I a new religious leader and movement made their appearance. Mani (216?–274?) was the offspring of a Parthian family resident in Babylonia (“a thankful disciple I am, risen from Babel’s land”) but was himself a speaker of Aramaic. Knowledge of his teachings was greatly increased by the discovery in the early 20th century of many fragments of Manichaean literature in eastern Turkistan. Subsequently a large part of the Kephalaia, a collection of the religious injunctions of Mani, was recovered in a Coptic version found in Egypt. These texts can now be collated with the versions of Manichaean doctrines as reported by the Church Fathers, including St. Augustine. From this cumulative documentation, to which other sources can be added, it appears, among other things, that Mani’s teachings were formulated under the strong influence of Gnostic ideas and philosophy. Mani proclaimed himself to be the last and greatest Apostle of Jesus as well as the Paraclete announced in the Gospel According to John. With the Gnostic interpretation of the Gospel, Mani tried to combine the doctrines of Zoroaster and Jesus in order to create a new religion of a universal character. There is a tradition that he made his first appearance as a teacher on the coronation day of Shāpūr (April 12, 240, or April 9, 243), but other evidence suggests that Mani was not necessarily in Iran at the time and may have been on a sea journey to India when he started preaching. He later returned and found many followers, among whom were Fīrūz (Pērōz) and Mihrshāh, governor of Maishān (Mesene), both brothers of Shāpūr. Even the king himself is said to have been impressed and to have granted the prophet several personal interviews. On the last such occasion, Mani presented the king with his first book, the Shāpuragān (Shabuhragan), a summary of his teachings (“dedicated to Shāpūr”) written in the Middle Persian language, which provides further evidence of a degree of royal favour. During Shāpūr’s reign the religion of Mani was thus propagated in and beyond Iran. The heir to the throne, Hormizd I, was also favourably disposed toward him. Shāpūr’s younger son, Bahrām I, however, yielded to pressure from the priestly establishment, and Mani was executed. After that, Manichaeism was persecuted and destroyed in Iran. Yet it maintained itself not only in the West, penetrating far into the Roman Empire, but also in the East, in Khorāsān and beyond the boundaries of the Sāsānian empire. There the seat of its leader was at Samarkand, whence it penetrated Central Asia. Art and literature
Perhaps the most characteristic and certainly among the most impressive relics of Sāsānian art are the great rock sculptures carved on the limestone cliffs that are found in many parts of the country. The best-known groups are at Naqsh-e Rostam and Naqsh-e Rajab, both near Persepolis, and at Bishāpūr, an ancient city a few miles north of Kāzerūn in Fārs. At Fīrūzābād—the ancient Gūr, also in Fārs—are two reliefs of Ardashīr I, one depicting the overthrow of Artabanus V, the other depicting an investiture scene. Not far away, in the valley at Sar Mashhad, a representation of Bahrām II shows that king in the process of slaying two lions. At Dārābgerd, about 180 miles (290 km) southwest of Shīrāz, Shāpūr I is shown triumphing over three Roman emperors—Gordian III, Philip the Arabian, and Valerian. At Naqsh-e Bahrām, north of Kāzerūn, Bahrām III is depicted enthroned. The same ruler appears at Qaṣr-e Abū Nasr, near Shīrāz, and at Gūyom, not far from there. Sāsānian sculptured reliefs are less numerous outside Fārs, but a Sāsānian equestrian that once existed at Rayy (ancient Rhagae), southeast of modern Tehrān, was replaced in the 19th century by a representation of Fatḥ ʿAlī Shāh, a member of the then-ruling Qājār dynasty. At Salmās, near Lake Urmia, Ardashīr I is shown on horseback while receiving the surrender of a Parthian personage. There are also later Sāsānian sculptures at Ṭāq-e Bostān, near Kermānshāh, showing Ardashīr II, Shāpūr III, and Khosrow II. In many of these representations the Sāsānian kings can be identified by their individual crowns.
The most ambitious and celebrated architectural achievement of the dynasty is the vast palace at Ctesiphon, built by Khosrow II (590; 591–628), a part of which is still standing. It is known as the Ṭāq Kisrā and is notable for its great barrel vault in baked brick, a typically Sāsānian architectonic device. Many Sāsānian buildings can also be seen in Fārs, where the characteristic construction is of limestone blocks embedded in strong mortar. The most important of these are near Shīrāz: the palace of Ardashīr I to the south at Fīrūzābād and a small, well-preserved palace at Sarvestān, southeast of Shīrāz, in which the rooms are roofed with domes and squinches, features often found in Sāsānian architecture. Excavations at Bishāpūr, or Shāhpūr, have revealed some mosaic floors and other features of this important Sāsānian town. Numerous fire temples of the period survive, especially in Fārs; these are square buildings roofed by a dome over four arches. Sāsānian remains of considerable extent also exist at Qaṣr-e Shīrīn, on the road from Baghdad to Tehrān, and at Gondēshāpūr, modern Shāhābād, south of Dezfūl.
Generally speaking, the Sāsānian era was one of a renaissance in Iranian art, which, if not quite on the same level as the Achaemenian achievement, was of no small importance. Metalwork reached a high level of artistry and craftsmanship; its most characteristic decorative themes are hunting scenes portraying the Sāsānian kings in action. A gold and enamel drinking vessel (now in the Bibliothèque Nationale in Paris) from the time of Khosrow I—known as the Cup of Solomon and, according to one tradition, a gift from the caliph Hārūn al-Rashīd to Charlemagne—is perhaps the most sumptuous specimen of Sāsānian metalworking. The art of gem engraving produced many fine intaglio stamp seals and cameos. The coins invariably bear a Pahlavi inscription; on the obverse (see photograph) is the head of the king, wearing his characteristic crown, accompanied by his name and title, while on the reverse is the fire altar with its guardians and a legend such as “Fire of Ardashīr” or “Fire of Shāpūr” or, in the later period, an abbreviated mint name and the regnal date. (For additional discussion of Sāsānian visual arts, see art and architecture, Iranian.)