The early death of Alexander the Great in 323 BCE, without an effective heir, was followed by a conference of his leading generals (who would come to be known as the “Successors”) as to what should be done. The senior of them, Perdiccas, was appointed regent of the empire, and the other generals became satraps (governors) of major provinces. The most important of these were located in the western half of Alexander’s empire – Macedonia, Greece, Asia Minor, Syria, Mesopotamia and Egypt. The eastern satrapies (provinces) in Iran, central Asia and India were left in the hands of less important commanders.
This arrangement (the “Partition of Babylon”, as it is called) did not last long. The Successors started falling out with one another almost immediately. Perdiccas was assassinated, wars flared up and a fierce struggle for dominance (or survival) followed, in the twists and turns of which the control of the different satrapies changed hands frequently. In the course of these turns of fate a commander called Seleucus gained control of the satrapy of Babylon.
(For background to these events see Alexander the Great and the Hellenistic World.)
By this time (312 BCE) a power vacuum had arisen in the eastern provinces, as the satraps there had either fallen in battle with each other or died in some other way. From his base in Babylon Seleucus skillfully filled this vacuum by sending his forces into these areas and taking control of them. He beat off attempts by other powerful Successors (who were mainly concerned with fighting for dominance in the west) to dislodge him, and by 302 BCE he ruled a vast area from eastern Mesopotamia to western India.
In 306 Seleucus had taken the title of king, following the example of the other Successors. He had also founded a new capital, near Babylon, which he called Seleucia-on-the-Tigris.
The following year Seleucus came to an arrangement with Chandragupta, the king of the rising Mauryan empire in India, whereby he ceded his Indian provinces in return for 500 war elephants.
At the Battle of Ipsus, in 301 BCE, which was between various of the Successors, a decisive charge by Seleucus’ elephants helped ensure that he was on the winning side. One result of this was that the use of war elephants spread to other Hellenistic armies. Another more immediate result was that Seleucus gained Syria and parts of eastern Asia Minor.
He was now one of the two most powerful Successors left standing. The other one, Lysimachus, had started as king of Thrace and then gained Macedonia and much of Greece and Asia Minor. Finally, some twenty years later, Seleucus and Lysimachus met at the battle of Crupedium, in Asia Minor (281 BCE). In this, Seleucus (by then in his late 70s) defeated and killed Lysimachus.
Seleucus now ruled a vast kingdom stretching from Bactria in the east to Asia Minor in the west. He apparently had even wider ambitions, intent on reunifying Alexander the Great’s empire under his rule; however he was assassinated very shortly after his victory over Lysimachus, as he crossed over to Macedonia.
After Seleucus’ death in 281 BCE, his sprawling empire was ruled by his descendants. The empire had two capitals. Antioch-on-the-Orontes in Syria had been founded by Seleucus in 300 BCE and from here the western parts were governed. Seleucia-on-the-Tigris in Mesopotamia was the center of government in the east. These two would both grow into enormous cities by the standards of the time, both benefitting not just from their role as centers of government but of commerce as well, being situated on the main east-west trade routes of the period. In the early Hellenistic period Seleucia was the large of the two capitals, but later, as Seleucid power shifted decisively to Syria, Antioch would come outshine it; it was reckoned to rival Alexandria, in Egypt, as one of the leading cities of the Hellenistic world, with a population of 500,000.
These two cities were only the largest of many Greek-style cities which the Seleucids founded right across their realm. These were settled by Greek and Macedonian immigrants, and later by elements of the local populations who adopted Greek language and culture wholesale. Such cities formed centers of the hybrid Greek/Asian civilization, which we call Hellenistic, which was spreading around the Middle East at this time. Some ancient cities in the Middle East (or their elites, at any rate), such as the great Phoenician city of Tyre, would also adopt much Greek culture, whilst others remained centers of older cultures. The Seleucid period saw cities such as Uruk build new temples and ziggurats, or refurbish old ones, in the traditional Mesopotamian style.
Under the early Seleucids, the empire was organized along the same lines as Alexander’s empire, and before that the Persian empire. Powerful satraps governed large provinces (satrapies), and in some places sizable territories were ruled by hereditary dynastic families who acknowledged the Seleucid king as their overlord. At a lower level of administration, districts were ruled (under theoretical satrapal supervision) by local dynastic families, or were allocated to the numerous new Greek-style cities which had sprung up around the empire.
The first of Seleucus’ successors was his son, Antiochus I (reigned 281-261 BCE). He had to deal with multiple threats to his empire. In 276 a large body of Gauls, who had terrorized Macedonia and Greece, crossed into Asia Minor. Here they were defeated by Seleucid forces, and Antiochus settled them in a region of central Asia Minor which would henceforth be known as Galatia. The Gauls acknowledged him as their overlord.
Between 274-271 Antiochus also fought the first of several wars between the Seleucids and the Ptolemies of Egypt, over control of the Levant and Judaea. This achieved little for either side.
The ramshackle Seleucid state soon began to shed territory. Vassal kings and satraps began to assert their independence from Seleucid rule. In Asia Minor the kingdoms of Cappadocia, Bithynia and Pontus, and in the east the satrapies of Bactria and Parthia, were all effectively independent by around the mid-3rd century BCE. Parthia was soon after invaded and occupied by the Parni, an Iranian tribe from central Asia, who were henceforth known as the Parthians.
The Seleucid kings were hampered in dealing with these break-aways by internal troubles – rivalries between different members of the royal house and indecisive but costly wars with Ptolemaic Egypt: Antiochus II (reigned 261-246 BCE) fought a second indecisive war with Ptolemaic Egypt, while Seleucus II (reigned 246-225 BCE) fought and decisively lost a third war with it (246-241 BCE).
The Gauls continued to menace neighboring lands in Asia Minor from time to time until in 238 BCE they were severely defeated, not by the Seleucid king but by a local vassal, Attalus, whose family had controlled the city of Pergamum for a couple of generations. From then on the Gauls confined themselves to their own territory of Galatia, but where essentially independent from the Seleucids under their own kings. Attalus, meanwhile, declared his independence of the Seleucids by proclaiming himself king of Pergamum. This kingdom would gradually expand its territory in western Asia Minor, but would always remain quite small. However, it was extremely wealthy, and was able to punch above its weight in the international affairs of the region.
Seleucus II was also unable to prevent the satrapy of Media from breaking away, let alone bringing other territories back under Seleucid rule.
Antiochus III (the Great, reigned 222-187 BCE) succeeded in turning the tide, at least for a time. He conducted several vigorous campaigns to retake the lost provinces of the empire, including Parthia and Bactria, and through war and diplomacy was able to bring them back into at least nominal vassalage and receive tribute from their rulers. In a fourth war with the Ptolemies (219-217 BCE) he was also able to conquer Palestine and the Levant, which had been under Egyptian control since the wars of the Successors.
By this time another power had appeared in the west: Rome. Antiochus now turned his attention west by posing as a champion of the city-states of Greece against the Romans, and in the war that inevitably followed he was heavily defeated at the battles of Thermopylae (191) and Magnesia (190). This cost him all his gains in Asia Minor and a huge indemnity. The satrap of Armenia also broke away from the Seleucid empire, and the eastern satrapies soon reasserted their independence.
Antiochus IV Epiphanes (reigned 187-164 BCE) is famous for trying to impose the Greeks’ pagan religion on the Jews in Judaea, thus provoking them into rebellion. This led eventually to the setting up of an independent Jewish state centered on Jerusalem. This state would have an ambiguous relationship with the rest of the Hellenistic world; its ruling class was deeply influenced by Greek thought and culture, but strict Jews, who were numerous and influential, abhorred the pagan beliefs and practices of the Greeks.
Antiochus died on a campaign against the Parthians, who were raiding his eastern territories. This was a failure, and from the 140s the Parthians started expanding rapidly. They had soon conquered all the eastern satrapies of the Seleucid empire and in 141 BCE the eastern capital of Seleucia fell to them. Succeeding Seleucid kings attempted to restore their power in the East, but all failed: Demetrius II was taken captive by the Parthians (139) and Antiochus VII was killed in an ambush (129). So ended all Seleucid ambitions in that region; the Seleucid kingdom was henceforth confined to Syria, with Antioch as its single capital.
In 133 BCE, when king Attalus III of Pergamum died without an heir, to spare his subjects a civil war or invasion from neighboring states he handed his kingdom to the Roman Republic in his will. This became the Roman province of Asia. By the end of the 2nd century BCE the Romans had become the dominant power in throughout the Mediterranean.
The Seleucid kingdom, now confined to Syria, was beset by recurrent civil wars. Such as its weakness that it was largely ignored by both sides in the long wars between the Romans and Mithridates of Pontus (88-65 BCE). However, the king of Armenia, Tigranes the Great, invaded and took control of Syria in 83 BCE. Siding with Mithridates against the Romans, Tigranes was defeated by the latter and forced to cede Syria back to the Seleucids (69 BCE). The Seleucids immediately descended into civil war again, and in 63 BCE the Romans, now in complete control of the region after their final defeat of Mithridates, annexed Syria as a Roman province.