Mesopotamia is scarcely mentioned in the Greek sources relating to the Seleucids, because the Seleucid rulers were occupied with Greece and Anatolia and with wars with the Ptolemies of Egypt in Palestine and Syria. Even the political division of Mesopotamia is uncertain, especially since Alexander, Seleucus, and Seleucus’ son Antiochus I Soter all founded cities that were autonomous, like the Greek polis. The political division of the land into 19 or 20 small satrapies, which is found later, under the Parthians, began under the Seleucids. Geographically, however, Mesopotamia can be divided into four areas: Characene, also called Mesene, in the south; Babylonia, later called Asūristān, in the middle; northern Mesopotamia, where there was later a series of small states such as Gordyene, Osroene, Adiabene, and Garamea; and finally the desert areas of the upper Euphrates, in Sāsānian times called Arabistān. These four areas had different histories down to the Arab conquest in the 7th century, although all of them were subject first to the Seleucids and then to the Parthians and Sāsānians. At times, however, several of the areas were fully independent, in theory as well as in fact, while the relations of certain cities with provincial governments and with the central government varied. From cuneiform sources it is known that traditional religious practices and forms of government as well as other customs continued in Mesopotamia; there were only a few Greek centres, such as Seleucia and the island of Ikaros (modern Faylakah, near Kuwait), where the practices of the Greek polis held sway. Otherwise, native cities had a few Greek officials or garrisons but continued to function as they had in the past.
Seleucia on the Tigris was not only the eastern capital but also an autonomous city ruled by an elected senate, and it replaced Babylon as the administrative and commercial centre of the old province of Babylonia. In the south several cities, such as Furat and Charax, grew rich on the maritime trade with India; Charax became the main entrepôt for trade after the fall of the Seleucids. In the north there was no principal city, but several towns, such as Arbela (modern Irbīl) and Nisibis (modern Nusaybin), later became important centres. In the desert region, “caravan cities” such as Hatra and Palmyra began their rise in the Seleucid period and had their heyday under the Parthians.
The only time that the Seleucid kings lost control of Mesopotamia was from 222 to 220 bce, when Molon, the governor of Media, revolted and marched to the west. When the new Seleucid king, Antiochus III, moved against him from Syria, however, Molon’s forces deserted him, and the revolt ended. The Parthians, under their able king Mithradates I, conquered Seleucid territory in Iran and entered Seleucia in 141 bce. After the death of Mithradates I in 138 bce, Antiochus VII began a campaign to recover the Seleucid domains in the east. This campaign was successful until Antiochus VII lost his life in Iran in 129 bce. His death ended Seleucid rule in Mesopotamia and marked the beginning of small principalities in both the south and north of Mesopotamia.
Seleucid rule brought changes to Mesopotamia, especially in the cities where Greeks and Macedonians were settled. In these cities the king usually made separate agreements with the Greek officials of the city regarding civil and military authority, immunity from taxes or corvée, or the like. Native cities continued with their old systems of local government, much as they had under the Achaemenians. Greek gods were worshiped in temples dedicated to them in the Greek cities, and native Mesopotamian gods had temples dedicated to them in the native cities. In time, however, syncretism and identification of the foreign and local deities developed. Although the policy of Hellenization was not enforced upon the population, Greek ideas did influence the local educated classes, just as local practices were gradually adopted by the Greeks. As in Greece and the lands of the eastern Mediterranean, in Mesopotamia the philosophies of the Stoics and other schools probably had an impact, as did mystery religions; both were hallmarks of the Hellenistic Age. Unfortunately there is no evidence from the east on the popularity of Greek beliefs among the local population, and scholars can only speculate on the basis of the fragmentary notices in authors such as Strabo. The Seleucid rulers respected the native priesthoods of Mesopotamia, and there is no record of any persecutions. On the contrary, the rulers seem to have favoured local religious practices, and ancient forms of worship continued. Cuneiform writing by priests, who copied incantations and old religious texts, continued into the Parthian period.
The administrative institutions of the countryside of Mesopotamia remained even more traditional than those of the cities; the old taxes were simply paid to new masters. The satrapy, much reduced in size from Achaemenian times, was the basis for Seleucid control of the countryside. A satrap or strategus (a military title) headed each satrapy, and the satrapies were divided into hyparchies or eparchies; the sources that use these and other words, such as toparchy, are unclear about the subdivisions of the satrapy. There was a great variety of smaller units of administration. In the capital and in the provincial centres, both Greek and Aramaic were used as the written languages of the government. The use of cuneiform in government documents ceased sometime during the Achaemenian period, but it continued in religious texts until the 1st century of the Common era. The archives were managed both in the capital and in provincial cities by an official called a bibliophylax. There were many financial officials (oikonomoi); some of them oversaw royal possessions, and others managed local taxes and other economic matters. The legal system in the Seleucid empire is not well understood, but presumably both local Mesopotamian laws and Greek laws, which had absorbed or replaced old Achaemenian imperial laws, were in force. Excavations at Seleucia have uncovered thousands of seal impressions on clay, evidence of a developed system of controls and taxes on commodities of trade. Many of the sealings are records of payment of a salt tax. Most of the tolls and tariffs, however, were local assessments rather than royal taxes.
Artistic remains from the Seleucid period are exceedingly scarce, and, in contrast to Achaemenian art, no royal or monumental art has been recovered. One might characterize the objects that can be dated to the Seleucid era as popular or private art, such as seals, statuettes, and clay figurines. Both Greek and local styles are found, with an amalgam of styles prevalent at the end of Seleucid rule, evidence of a syncretism in cultures. The numerous statues and statuettes of Heracles found in the east testify to the great popularity of the Greek deity, in Mesopotamia identified with the local god Nergal.