Nicator Seleucus I., the founder of the Syrian monarchy, and of the dynasty of the Seleuci-dae, born about 358 B. C, assassinated at Ly-simachia in 280. He was the son of Antiochus, one of the generals of Philip of Macedon, and accompanied Alexander in his Asiatic expedition. After the death of that monarch he adhered to the fortunes of Perdiccas, but soon after headed his assassins at Pelusium (321). On the second division of the empire he received the satrapy of Babylonia, joined An-tigonus against Eumenes, and received from the former the government of Susiana. Anti-gonus very soon became jealous of his power, and planned his destruction. Seleucus escaped with about 50 horsemen, fled to Egypt, and formed a league with Ptolemy, Lysimachus, and Cassander against the common enemy. Seleucus regained possession of the government of Babylonia in 312, and from this year the Syrian monarchy is reckoned to commence. In 306 he assumed the title of king, and in 302 joined the new league formed by Ptolemy, Cassander, and Lysimachus against Antigo-nus. The war was ended by the victory of the allies at Ipsus in 301, when Antigonus was killed, and Seleucus obtained all the Asiatic territory conquered by the Greeks, with the exception of lower Syria and western Asia Minor. His empire, extending over about 1,000,000 sq. m., included parts of Cappado-cia and Phrygia, Armenia, upper Syria, Mesopotamia, Media, Assyria, Babylonia, Susiana, Persia, Parthia, Bactria, and the territory eastward, probably including some parts of India. He founded the city of Seleucia on the Tigris, and removed the seat of government thither; but soon after the battle of Ipsus he made Antioch his capital.

The change offended most of his Asiatic peoples, and served to hasten the disintegration of his dominions. The dissatisfaction increased when he divided the empire into 72 satrapies, setting over each a Macedonian or Greek. He afterward allied himself with Demetrius Poliorcetes, the son of Antigonus, whose daughter Stratonice he married; but Demetrius having made himself king of Macedonia, Seleucus joined the alliance against him in 288, and took possession of the greater part of his Asiatic dominions. Demetrius surrendered to him in 286, and remained at Apamea in Syria till his death. At the instigation of the widow of Agathocles, put to death by his father Lysimachus, Seleucus invaded the dominions of his rival with a large army. Lysimachus met him in a decisive battle on the plain of Corus in Phrygia in 281, and was routed and slain. Seleucus now determined to add Macedonia to his dominions, and crossed the Hellespont with a large army, but was assassinated by Ptolemy Cerau-nus. He was succeeded by his son Antiochus. He founded Greek colonies in almost every province of his empire. - The dynasty of the Seleucidae lasted 247 years, from 312 to 65 B. C. The most important successors of Seleucus were his son Antiochus I., 280-261; Antiochus II., 261-246; Antiochus III., the Great, 223-187; and Antiochus IV., Epi-phanes, 175-164. The vast empire of Seleucus I. constantly diminished in power and extent, until it was finally absorbed by the Roman empire. - The era of the Seleucidae in chronology, is considered as beginning Oct. 1, 312 B. C. It was used in Syria, and by Jewish and Arab historians, until the 15th century.