The siege of Athens (to 404 BC) was the final act of the Great Peloponnesian War, and confirmed the Spartan victory that had been made almost inevitable at the naval battle of Aegospotami in 405 BC.
Athens had been on the defensive since suffering a major disaster at Syracuse in 413 BC, but she had won a number of victories in the intervening years, and her position looked to have improved. In reality Athenian power was increasingly precarious, especially since the Spartans began to built and improve their own fleet and gained support from Persia. Things came to a head in the Hellespont in 405 BC. A Peloponnesian fleet under Lysander moved into the Hellespont, and was followed by the last major Athenian fleet. This fleet was almost completely destroyed in the disastrous battle of Aegospotami, and only ten of the one hundred and eighty ships in the Athenian fleet survived.
News of this disaster reached Athens on the state trireme 'Paralus'. The Athenians were used to having a Spartan army close by on land, and had repulsed a number of direct attacks on the city in recent years, but now they faced the prospect of being blockaded from the sea as well. Little or no outside help could be expected, and the fall of Athens seemed inevitable. The Athenians were now uncomfortably aware of their harshness towards many captured cities during the war, and began to imagine the city destroyed and its population killed or sold into slavery. Work began on blocking the harbours and improving the walls.
Three Peloponnesian forces now converged on Athens. King Agis had an army at Deceleia, in Attica, and so was closest to the city. King Pausanias, the second Spartan king, raised a new army in the Peloponnese and marched on Athens. Finally Lysander appeared off the Piraeus at the head of a fleet of 200 ships.
The defences of Athens actually held out quite well against this test, but it was clear that starvation would soon force the city to surrender, and the Athenians began peace negotiations.
Their first peace offer was very optimistic. The Athenians offered to become allies of Sparta as long as they were allowed to keep their fortifications and the Piraeus. These terms were turned down by the ephors, who demanded that the Athenians demolished at least one mile of the long walls connecting the city to the sea at Piraeus. In the early stages of the siege these terms were unacceptable, and the assembly even passed a decree making it illegal to propose demolishing the walls.
After this decree was passed Theramenes offered to go to Lysander and find out why the Spartans wanted the walls demolished. He stayed in the Spartan camp for three months, and on his return was appointed as one of then ambassadors who were sent to Sparta with full powers to negotiate surrender terms.
Theramenes and his fellow ambassadors eventually reached Sparta, where the surrender terms were discussed before a general assembly, with Sparta's allies present. Corinth and Thebes were at the head of a party that wanted to see Athens destroyed, but the Spartans were more moderate. Their argument was that Athens was a key part of the Greek world, and had played a noble part in the defence against Persia.
The Spartan terms were surprising generous. Athens would remain an independent city, but she would have to become an ally of Sparta, following her lead in diplomacy and supporting her in war. The long walls and the fortifications of Piraeus were to be destroyed. The Athenian navy was to be almost destroyed, and was reduced in size to only twelve ships. Finally all exiles were to be allowed to return to the city.
The ambassadors returned to an Athens that was on her last legs, with large numbers dying daily of starvation. The Spartan terms were accepted by a large majority of the people, and the Great Peloponnesian War finally came to an end. Lysander led his fleet into the Piraeus, and began work on demolishing the walls.
Sparta emerged from the long wars victorious, but her dominance in Greece would be short-lived. Spartan attempts to take Athens's position around the Aegean failed, and within a few years all of the restrictions on Athens had been removed, while an attempt to replace the democracy was very short-lived. For a brief time Athens, Thebes and Corinth were even allied against Sparta (Corinthian War, 395-387 BC). The most important long term result of the war was that it ended any chance of Athens becoming a major Imperial power, and left a power vacuum that would be filled by Macedonia.