The Seleucid Empire was one of several political states founded after the death of Alexander the Great, whose generals squabbled over the division of Alexander's empire.
The Seleucid Empire, founded in 323 BC by Seleucus I, controlled a large region including Mesopotamia, Persia (eastward to the Indus River), modern-day Syria, Lebanon, and Jordan. The Seleucid Empire lost much territory just prior to and during the 2nd century BC; Gedrosia on the coast of the Arabian Sea and Arachosia on the west bank of the Indus were ceded to Chandragupta in 303 BC; Bactria asserted independence in 250 BC, followed by Parthia ten years later. Antiochus III is considered the greatest of the Seleucid monarchs, but his campaigns in Greece in 192 BC attracted the attention of the Roman Empire, after which the Seleucids declined.
See Seleucid dynasty