The Second Syrian War is one of the worst documented of all Hellenistic wars. We are not entirely sure why it started; we can not construct a clear narrative of events. There is even some uncertainty as to the date of the main battle of the war. We do know what the results of the war were, and we have some snapshots of events. These events suggest that this was a major war, involving all three of the main successor states – Macedonia, Egypt and the Seleucid Empire – with fighting in Asia Minor, the Aegean, Syria, North Africa and possibly in Greece.
As a result of the First Syrian War, Ptolemy II had gained possession of large parts of the coast of Asia Minor, giving Egypt a strong base in the Aegean. These victories had largely been at the cost of Antiochus I, the Seleucid Emperor. He died in 261 and was succeeded by his younger son, Antiochus II. The Second Syrian War may have begun as an attempt by Antiochus II to regain lost lands.
Another possible cause was a rebellion by Ptolemaeus, the son of Lysimachus and adopted son of Ptolemy II. He had a claim to the throne of Macedonia, and had hoped that Ptolemy would help him win that throne, but by 260 it was clear that that would not happen. Accordingly, in 260 Ptolemaeus rebelled against Ptolemy from a base at Ephesus. At first Antiochus welcomed the rebellion. He sent Ptolemaues a number of Thracian troops, and may have offered him the support of his commander in Miletus, an Aetolian Greek called Timarchus. It would appear that Ptolemaeus and Timarchus soon got out of control. Ptolemaeus was murdered, probably in 259 BC, and Antiochus occupied Ephesus. Timarchus then declared himself Tyrant of Miletus. Antiochus was forced to march against Timarchus, deposing him in 258 BC, and restoring the traditional constitution of Miletus, where he was then worshiped.
The main battle of the war was a naval battle, fought off Cos, probably in 258 BC. Ptolemy had the stronger fleet and was normally allied with Rhodes, which possessed the best fleet in the eastern Mediterranean. Worried by Ptolemy’s aggression, Rhodes decided to side with Antiochus and Antigonus. Their fleet had played a part in the capture of Ephesus and at the battle of Cos. This was fought between the Egyptian fleet and the Macedonian fleet, actually commanded by King Antigonus. The date of this battle is not entirely secure, but it was known to have taken place during the Isthmian Games, which took place every two years, limiting it to either 258 or 256 BC, the earlier date being seen as more likely. Egypt had the larger fleet, but the Macedonians seem to have concentrated on boarding tactics, and won an important victory.
With Egyptian sea power temporarily removed, Antigonus and Antiochus had the upper hand in the war. Antiochus was able to recapture most of the territory lost in the First Syrian War in Asia Minor (expelling Ptolemy from Cilicia and Pamphylia, as well as northern Phoenicia as far as Sidon. Antigonus gained control of the Island League, although Ptolemy retained Thera (modern Santorini).
The peace between Antiochus and Ptolemy was soon cemented by a marriage between Antiochus and Ptolemy’s daughter Berenice Syra. To do this he had to repudiate his first wife, Laodice. This soon led to disaster. In 247 Antiochus died, followed early in 246 by Ptolemy II. Both Berenice and Laodice claimed the Seleucid throne for their son. Ptolemy III intervened in favour of his sister, but she was then murdered by supporters of Berenice. The result was the Third Syrian War.