After defeating Demetrius at Gaza and then taking Babylonia the same year, Seleucus I established the power base conventionally used to date the beginning of the Seleucid Empire.
Seleucus founded Seleucia on the Tigris (near modern Baghdad) as a major administrative and economic center; it served as the first Seleucid capital and remained a key metropolis even after the political center shifted west.
Seleucus campaigned in the Indus borderlands against Chandragupta Maurya; the conflict ended with a diplomatic settlement that included territorial concessions by Seleucus and receipt of war elephants, helping secure his eastern frontier.
In the coalition victory at Ipsus, Antigonus I was defeated, enabling Seleucus to consolidate key western territories (notably in Syria and Anatolia) and making the Seleucid realm a principal Hellenistic power.
Seleucus founded Antioch on the Orontes, which developed into one of the eastern Mediterranean’s largest cities and later served as the Seleucid imperial capital for much of the dynasty’s history.
Seleucus’ victory over Lysimachus at Corupedium marked the last major showdown among Alexander’s immediate successors and briefly expanded Seleucid control into Anatolia.
Antiochus III (“the Great”) came to the throne and initiated a major effort to restore Seleucid strength after decades of fragmentation, including reforms and large-scale campaigns across the empire.
At Raphia, Antiochus III suffered a major defeat against Ptolemy IV during the Fourth Syrian War, temporarily checking Seleucid ambitions in Coele-Syria.
Antiochus III defeated Ptolemaic forces near Panium, a turning point of the Fifth Syrian War that brought Coele-Syria under lasting Seleucid control.
In the Roman–Seleucid War, Antiochus III was decisively defeated by Roman and Pergamene forces at Magnesia, ending Seleucid dominance in Asia Minor.
The peace settlement with Rome forced Antiochus III to abandon territory west of the Taurus, surrender war elephants and most of his fleet, and pay a large indemnity—reducing the empire largely to Syria, Mesopotamia, and parts of Iran.
Antiochus IV imposed coercive religious measures in Jerusalem, including erecting an altar to Zeus in the Temple and banning key Jewish rites; these actions helped trigger the Maccabean uprising.
Under Mithridates I, Parthia conquered Babylonia and held a formal investiture at Seleucia, signaling a decisive eastern break from Seleucid control and accelerating imperial contraction.
Antiochus VII Sidetes temporarily recovered parts of the eastern realm but was killed fighting the Parthians in 129 BCE, after which Seleucid power was effectively confined to Syria.
With Seleucid authority fractured by dynastic conflict, Tigranes II of Armenia intervened and assumed control in Syria, further eroding the dynasty’s remaining sovereignty.
Roman intervention under Pompey brought the remnants of Seleucid Syria under Roman rule; Syria was annexed as a Roman province, ending Seleucid kingship in practice.
Seleucid Empire (312–63 BCE)
