The siege of Perinthus (340-339 BC) was an unsuccessful attempt by Philip II of Macedon to defeat a wavering ally, and was conducted alongside an equally unsuccessful siege of Byzantium. Both sieges took place in the period just before the Fourth Sacred War.
Perinthus was officially allied with Philip, and in 340, when Philip decided to support his allies in the Chersonese against the local Athenian commander, he asked Perinthus and Byzantium to help. Both cities refused to offer support, and Philip decided to reduce them to obedience before dealing with the Athenians.
Perinthus was a difficult target for a siege. The city stood on a promontory, connected to the land by a 200 yard wide heavily fortified isthmus. The coast was protected by cliffs, making any amphibious assault impossible. The promontory was covered by houses rising steeply on terraces, and the promontory was protected by strong fortifications.
Philip had an impressive siege train, created by the Thessalian siege engineer Polyeidus. He built 120ft high siege towers, topped with catapults, battering rams and mines, and battered the outer walls.
The defenders were supported by Byzantium, which sent men and catapults. The Athenian fleet, under Chares, managed to keep the Macedonian fleet out of the Propontis, so the defenders had control of the seas around the city. The Persians also sent help, a force of Greek mercenaries under the Athenian Apollodorus.
Philip decided to send part of his army to escort the fleet through the Hellespont. Probably at about the same time he sent a letter to Athens, condemning the city's hostile attitude and appealing for restraint. This was never likely to have any impact at Athens, but any chance was eliminated by the progress of a Macedonian army along the coast of the Athenian territory in the Chersonese.
Although this did allow Philip to get his fleet into the Propontis, that didn't make any difference. The defenders were now getting support from the Persians, after Artaxerxes III ordered his satraps to send aid. Reinforcements and supplies reached the city, and the Macedonian fleet was unable to intervene.
After several weeks of active siege work the Macedonians finally breached the outer wall, but to their dismay they discovered that the defenders had walled up the gaps between the first line of houses, creating a fresh, almost equally strong line of defences.
Philip now decided to shift his attention to Byzantium, in the hope that the aid she had sent to Perinthus would make her vulnerable. He left part of his army to blockade Perinthus, and moved the rest of it to attack Byzantium. Early in this siege he intercepted a Athenian merchant fleet, capturing 180 Athenian ships. This move finally triggered a declaration of war by Athens, and the Athenians provided open support to the defenders of Byzantium.
Philip continued with both sieges across the winter of 340-339 BC, but after one last failed assault on Byzantium decided to abandon both and instead carried out a campaign in the Balkans.
Perinthus was soon forced to come to terms to Philip, probably after the Athenians and Thebans suffered their great defeat at the battle of Chaeronea (338 BC), but retained some independence, and continued to issue her own coins.