The Phyle Campaign was the civil war that resulted from the Spartan imposition of a narrow oligarchy on Athens (Thirty Tyrants) and resulted in the restoration of Athenian democracy. The Thirty were short of funds and this led them to persecute wealthy Athenians of whatever political views. Many fled to Boeotia and Corinth who offered asylum in defiance of Sparta.
Due to both deference to Sparta and to their cash shortage the Thirty had left Athens' border forts ungarrisoned which allowed a group of Athenian exiles to seize the fort of Phyle in 404/403 BCE. The leader of the exiles, initially only some 70 strong, was Thrasybulus who had a reputation as a moderate democrat and so ideal to unite all democratic opponents of the thirty.
A force of Athenian cavalry and Spartans was sent against Phyle, but was defeated in two surprise attacks by Thrasybulus. Thrasybulus then marched on Piraeus.There, being too few to defend the entire port, he and his men seized one of its prominent hills, the Munychia.
The next morning, the forces of the Thirty marched out to meet them. The Athenian exiles drew up for battle in a formation ten ranks deep at the top of the Munychia, with light troops and spear throwers behind them. Below, in one of the markets of Piraeus, the joint Spartan-oligarchic force drew up in a formation of equal width, but fifty ranks deep. The Spartan garrison held the right, the forces of the Thirty the left. Xenophon's account of the battle states that Thrasybulus, to inspire his men, reminded them that the enemy right was composed of men who they had routed a few days before, while the left was made up of men who had wrongly driven them from their country.
The oligarchic forces advanced up the road towards the top of the hill, but before they reached the top the men from Phyle charged down the hill at them. This charge broke the oligarchic line, and the exiles pursued their enemies down the hill onto the level ground. In this rout, seventy men of the Thirty's force were killed. Among the dead was Critias, the leader of the Thirty; several other prominent oligarchic leaders were also killed.
After this battle, the prestige of the Thirty, already weakened by the earlier defeat near Phyle, was irreparably damaged. The next day the Thirty were deposed by a vote of the larger oligarchic governing body, the council of three thousand. The Thirty fled to Eleusis, and a governing board of ten was elected in their place. This new government, however, was not ready to compromise with the men in Piraeus, so envoys were sent to Sparta to request aid. Sparta first responded by sending Lysander with a force of mercenaries who clearly intended simply to place the thirty back in power. Very quickly, however, Sparta sent King Pausanias with a levy of the Peloponesian League.
Upon Pausanias's arrival in Attica, he ordered the men in Piraeus to disperse; when they refused to do so, he drew his men up to attack them, but did not actually engage them. The next day, however, a party of Athenian light troops attacked the Spartans while they were reconnoitering near Piraeus. Pausanias dispatched his cavalry and his youngest infantrymen to attack them, while he with the rest of the infantry followed in support. In pursuit, the Spartan cavalry and advance infantry entered Piraeus, where they encountered a large body of light troops, and were driven back with losses. Thrasybulus then came out with his hoplite force to press the issue; the Spartan hoplites engaged them, and, after a time, defeated them, inflicting 150 casualties. The men from Piraeus returned to the city, while Pausanias and his men returned to their camp.
After winning this victory, Pausanias, instead of pressing his advantage, sought to effect a reconciliation between the two Athenian parties. Accordingly, he persuaded both the men from Piraeus and the government in Athens to send emissaries to Sparta. These returned along with 15 officials empowered to work with Pausanias to negotiate a settlement to the issue. Pausanias then persuaded the Athenians to settle their disagreement on the terms of all being permitted to return to their homes except for the Thirty and their most prominent collaborators, while all who feared for their safety were free to remove to Eleusis. Democracy was reestablished, and all but the most egregious offenders were pardoned. Eleusis remained independent for a time, but, when it was revealed that the Thirty were gathering a mercenary army there, a preventive strike was launched and the town was reabsorbed into the Athenian state. Lysander's faction at Sparta was furious and along with King Agis brought Pausanias to trial to the end of 403 BCE. Fifteen of the Gerousia, including Agis, voted guilty and 14 against but all 5 Ephors voted non guilty so he was acquitted.