Editing Seleucus I Nicator (section)

==Admiral under Ptolemy (316–311 BC)==
{{Main|Third War of the Diadochi}}
After arriving in Egypt, Seleucus sent his friends to Greece to inform his fellow Diadochi Cassander (ruler of Macedon and overlord of Greece) and Lysimachus (ruler of [[Thracia]]) about Antigonus. Antigonus was now the most powerful of the ''Diadochi'', and the others would soon have to face him. Ptolemy, Lysimachus and Cassander formed a coalition against Antigonus. The allies sent a proposition to Antigonus in which they demanded shares of his accumulated treasure and of his territory, with Phoenica and Syria going to Ptolemy, Cappadocia and Lycia to Cassander, Hellespontine Phrygia to Lysimachus, and Babylonia to Seleucus.<ref>Diodorus Siculus, ''Bibliotheca Historica'' XIX 57,1.</ref> Antigonus refused, and in the spring of 314 BC, he marched against Ptolemy in Syria.<ref name="G55">Grainger 1990, pp. 53–55</ref> Seleucus acted as an admiral to Ptolemy during the first phase of the war. Antigonus was besieging [[Tyros|Tyre]],<ref>{{cite web |author=Jona Lendering |url=https://www.livius.org/di-dn/diadochi/war05.html |title=Alexander's successors: The Third Diadoch War |publisher=Livius.org |access-date=2012-11-07 |archive-date=18 November 2012 |archive-url=https://web.archive.org/web/20121118035712/http://www.livius.org/di-dn/diadochi/war05.html |url-status=dead }}</ref> when Seleucus sailed past him and went on to threaten the coast of Syria and Asia Minor. Antigonus allied with the island of [[Rhodes]], which had a strategic location and a navy capable of preventing the allies from combining their forces. Because of the threat of Rhodes, Ptolemy gave Seleucus a hundred ships and sent him to the Aegean Sea. The fleet was too small to defeat Rhodes, but it was big enough to force [[Asander]], the satrap of [[Caria]], to ally with Ptolemy. To demonstrate his power, Seleucus also invaded the city of [[Erythrai]]. [[Ptolemy (general)|Polemaios]], a nephew of Antigonus, attacked Asander. Seleucus returned to Cyprus, where Ptolemy I had sent his brother [[Menelaus (son of Lagus)|Menelaos]] along with 10,000 mercenaries and 100 ships. Seleucus and Menelaos began to besiege Kition. Antigonus sent most of his fleet to the Aegean Sea and his army to Asia Minor. Ptolemy now had an opportunity to invade Syria, where he defeated [[Demetrius I of Macedon|Demetrius]], the son of Antigonus, in the [[Battle of Gaza (312 BC)|battle of Gaza]] in 312 BC. It is probable that Seleucus took part in the battle. [[Peithon, son of Agenor]], whom Antigonus had nominated as the new satrap of Babylon, fell in the battle. The death of Peithon gave Seleucus an opportunity to return to Babylon.<ref name="G56">Grainger 1990, pp. 56–72</ref>

Seleucus had prepared his return to Babylon well. After the battle of Gaza Demetrius retreated to [[Tripoli, Lebanon|Tripoli]] while Ptolemy advanced all the way to [[Sidon]]. Ptolemy gave Seleucus 800 infantry and 200 cavalry. He also had his friends accompanying him, perhaps the same 50 who escaped with him from Babylon. On the way to Babylon Seleucus recruited more soldiers from the colonies along the route. He finally had about 3,000 soldiers. In Babylon, Peithon's commander, Diphilus, barricaded himself in the city's fortress. Seleucus conquered Babylon with great speed and the fortress was also quickly captured. Seleucus' friends who had stayed in Babylon were released from captivity.<ref name="G74">Grainger 1990, pp. 74–75</ref> His return to Babylon was afterwards officially regarded as the beginning of the [[Seleucid Empire]]<ref name=EB1911/> and that year as the first of the [[Seleucid era]].