The siege of Byzantium in 340-339 was an
unsuccessful attempt by Philip II to defeat a former ally, and was begun after
his siege of nearby Perinthus ran into
difficulties. Both sieges came in the build-up to the
Fourth Sacred War.
In around 343 a new Athenian commander, Diopeithes, was sent to the Chersonese,
to support the Athenian colonists in the area. He soon became involved in a
clash with Cardia, an ally of Philip's at the northern end of the Chersonese.
During this struggle Diopeithes rather overstepped the mark, capturing two
Macedonian heralds, and torturing and ransoming the second.
Unsurprisingly Philip decided to move to the area to try and support his
allies, and he called for help from Perinthus and Byzantium. Both cities were
allied with Philip, but he must have seemed a rather more threatening presence
since expanding his empire across most of Thrace, and both refused to help.
Philip responded by besieging Perinthus in 340-339. Byzantium sent supplies and
men to the besieged city, as did the Persians.
Philip's siege engines managed to break down the outer city wall, only to find
that the defenders had built a new wall between the first rows of houses.
Philip was also struggling at sea. At this stage he was officially at peace
with Athens, but the Athenians had prevented his fleet from passing through the
Hellespont. Eventually he decided to land his troops on the Chersonese, and use
them to escort the fleet through Athenian territory. Even this didn't help, and
after about three months Philip decided to launch a surprise attack on
Byzantium. In the late summer of 340 he led half of his army to Byzantium, but
the city turned down his offer of terms, and prepared to resist. Most of their
men and weapons were indeed at Perinthus, but the defenders managed to survive
the initial crisis. At about the same time an Athenian grain fleet was
gathering at Hieron, waiting for Chares to escort it to the
Aegean. While Chares was away meeting with local Persian officials, Philip's
fleet captured the merchant fleet. Fifty neutral ships were released, but 180
Athenian ships were captured. The supplies went to Philip's armies outside
Byzantium and Perinthus while the timber from the ships was used to build more
Philip then sent a letter to Athens in which he claimed that the merchant ships
had been supplying his enemies. This letter was treated as a declaration of war
in Athens, and open conflict between the two finally began. Chares was ordered
to use his forty ships to relieve Byzantium. The Macedonian fleet was forced to
retreat into the Black Sea, where it could neither help at the siege, nor
return to Macedon. Byzantium received help from her allies at Chios, Cos and
Rhodes, although the Persians don't appear to have intervened here, despite
having helped the defenders of Perinthus. At first the relationship between the
Byzantines and the Athenians wasn't good, as the Byzantines didn't trust
Chares. Things got better when a second fleet, commanded by Phocion and
Cephisophon, reached the area. Phocion and the Byzantine commander Leon were
personal friends, and they were able to coordinate a successful defence. The
Byzantines also received aid from their allies at Chios, Cos and Rhodes.
In the early spring of 339 Philip launched one last assault on the walls, using
the spring moonlight to aid a night attack. The barking of dogs was said to
have betrayed the attack, and Philip decided to give up and retreat. His
biggest problem was that his fleet was trapped in the Black Sea by an Athenian
force that held the Bosporus. Philip resorted to a simple trick to get his
fleet to safety. He sent a letter to Antipater, informing him that Thrace was
in revolt, and his garrisons under siege. Antipater was ordered to join Philip
as he marched into Thrace to restore control. The Athenians relaxed their guard
in the Bosporus, or possibly withdrew their fleet from the area, allowing
Philip to get his own fleet out of the Black Sea.
In both sieges Philip had the support of the great Thessalian siege engineer
Polyeidus, and had the most modern siege engines. His failure demonstrated how
hard it was to capture coastal cities if you didnt also have control of
the seas. Byzantium was soon forced to come to terms to Philip, probably after
the Athenians and Thebans suffered their great defeat at the battle of
Chaeronea in 338, although this might have come earlier. She retained enough
independence to continue to issue her own coinage.