The battle of Munychia (403 BC) was a significant victory for Democratic rebels against the Spartan imposed rule of the Thirty at Athens, and played a significant part in the reestablishment of Democracy at Athens in the aftermath of the Great Peloponnesian War.
After the end of the war the Spartan leader Lysander imposed an oligarchy on Athens. This Council of Thirty, soon known as the 'Thirty Tyrants', soon began a purge of their opponents, perceived opponents and any wealthy person outside the inner circle. Thousands were driven into exile, amongst the successful commander and democratic leader Thrasybulus, who fled to Thebes.
Early in 403 Thrasybulus and seventy followers seized the fort of Phyle, twenty miles north-west of Athens on the foothills of Mount Parnes. The Thirty led out their supporters, the 'Three Thousand', to attack Phyle, but their performance was poor. An initial attack on the fort was repulsed with ease, and an attempt to build a siege wall was foiled by heavy snow and a possible panic in the camp. The Thirty had the support of 700-750 Spartan hoplites, and they now sent those troops to blockade the fort. By now Thrasybulus had 700 men at his disposal, and he carried out a surprise dawn attack on the Spartan camp, inflicting an embarrassing defeat on them (battle of Phyle).
This relatively minor battle greatly affected the mood on both sides. The Thirty began to look for a refuge, and prepared for a move to Eleusis, and at the same time made an unsuccessful attempt to convince Thrasybulus to join them, offering him a place amongst the Thirty.
The Democrats were greatly encouraged by the victory, and by the arrival of fresh recruits. They soon had 1,000-1,200 men at Phyle, and Thrasybulus decided to take a gamble and try and capture Piraeus, the port of Athens. This had always been a hotbed of democratic support, and the Thirty had even exiled some of their opponents from Athens in the port. In the previous years the Spartans had insisted that the walls of Piraeus should be demolished, so the town was now unfortified.
Xenophon and Diodorus may give slightly different accounts of the move to Piraeus and the build up to the battle of Munychia. According to Xenophon the Democrats captured the port at night, without any fighting being mentioned. The Thirty led their troops down the road from Athens. The Democrats originally intended to defend the line of the town walls, but realised that they weren’t strong enough to hold such a long line, and instead drew up on the hill of Munichia,
According to Diodorus the Thirty gathered together their entire strength and camped in open countryside near Acharnae, six miles north of Athens, on the road to Phyle. Thrasybulus, now with 1,200 men at his disposal, advanced down the road and inflicted a defeat on the troops at Acharnae, forcing them to retreat back to Athens. This may actually be a slightly different account of the surprise attack on the Spartan camp near Phyle.
In both accounts, the Democrats ended up occupying a strong defensive position on the hill of Munychia, then an uninhabited hill to the north-east of Piraeus. The Thirty attacked this position and were defeated.
Diodorus gives a very short account of this battle. The Thirty had the advantage of numbers, the Democrats the stronger position. The battle was long and hard fought, but the tide turned after Critias, the leader of the Thirty, was killed. The oligarchic troops retreated back down the hill, and offered battle on the plains, but the Democrats refused to come down and attack. This encouraged many more Athenians to side with Thrasybulus, who was able to launch a surprise attack on the Oligarchs (after an unspecified time gap), defeat them, and take control of Piraeus.
In Xenophon the forces of the Thirty formed up at the market place of Hippodamus, and advanced up the hill in a formation fifty ranks deep. The Democrats formed up in a line of the same width, only ten ranks deeps, but with a significant number of lightly armed and missile troops behind them. A great deal of space is then dedicated to Thrasybulus's pre-battle speech, which gives us some details of the enemy formation. The remaining Spartans were on the right and the Thirty on the left. He then ordered his men not to attack first, because the seer had told them not to attack until one of them had been killed or wounded. The account of the battle itself is very short. The seer moved first and was killed. The Democrats were victorious, and pursued the oligarchs back to the level ground (just as in Diodorus). Amongst the dead were two of the thirty, Critias and Hippomachus, and of the Ten they had appointed to rule in Piraeus, and seventy more.
In the aftermath of this battle the Three Thousand turned on the remaining members of the Thirty and deposed them from power. They were replaced with a council of Ten, one from each tribe. Only two of the Thirty were part of the Ten, and the other survivors fled to Eleusis. There were now two centres of power on the oligarchic side, and they were increasingly outnumbered by the Democrats at Piraeus.
Both sets of oligarchs now called for help from Sparta. Lysander received permission to raise an army to help them, and arrived on the scene with remarkable speed, preventing the Democrats from pressing their attack on Athens itself. He was soon joined by the main Spartan army under King Pausanias, and the Spartans defeated the Democrats in battle at Piraeus. However the Spartans were politically divided themselves, and despite this victory Pausanias had no interest in seeing Lysander's friends take power in Athens. Instead he encouraged the Democrats, organised a reconciliation with the more moderate oligarchs, and oversaw the restoration of democracy at Athens.