The siege of Athens of 87-86 B.C. was one of the first major Roman successes during the First Mithridatic War (89-85 B.C.), and marked the point at which the initiative in the war began to move towards the Romans.
A Pontic army, under the command of the general Archelaus, had reached Greece during 88 B.C., coming at the invitation of the anti-Roman party in Athens, which at this time was led by the philosopher Aristion. With the support of Archelaus Aristion become dictator of Athens, and most of southern Greece came over to their cause, but a campaign in Boeotia faltered in the face of a small Roman army under the command of Q. Bruttius Sura, and Archelaus pulled back to Athens.
This gave Lucius Sulla time to reach Greece at the head of his consular army of five legions. After raising reinforcements in Aetolia and Thessaly, he advanced east through Boeotia towards Athens. By 86 B.C. the Long Walls, which had once connected Athens to Piraeus, were in ruins, and Sulla was faced with the problem of carrying out two sieges at the same time. Archelaus, with the main Pontic army, had decided to defend the port of Piraeus. Mithridates still had command of the sea, and so supplies and reinforcements could easily reach him.
Aristion had a more difficult job in Athens, which was closely blockaded by Sulla. While the Romans concentrated their efforts against Piraeus, the Athenians began to run short of food. At the start of the winter of 87-86 B.C. Sulla withdrew most of the forces around Piraeus into winter quarters at Eleusis, but maintained the blockade of Athens. Archelaus made an attempt to break this blockade, while his brother Neoptolemus launched a diversionary attack from his base at Chalcis, but both efforts failed.
In the spring of 86 B.C. Sulla decided to concentrate his efforts against Athens, where starvation was beginning to take hold. Aristion was also becoming increasingly unpopular within the city, partly because of his own conduct and partly because he had clearly led Athens close to disaster.
Sulla's main attack was launched at the area between the Sacred and Piraeic Gates, where he had discovered that the defences were at their weakest. On 1 March 86 B.C. Sulla's men broke into the city. The city was brutally sacked, although Sulla forbade his men from burning the city itself. The biggest fire was at the Odeum, burnt down by Aristion to prevent the Romans from using the timber it contained to attack the Acropolis.
When the city fell Aristion and his remaining supporters retreated to the Acropolis, where they managed to hold out for several weeks. The fall of the main city allowed Sulla to concentrate his efforts against Piraeus. Archelaus was forced to pull back into the peninsula of Munychia, which was protected on three sides by the sea. Although he could have held out here for much longer, Archelaus realised that there no point in doing so, and withdrew his surviving men onto their ships, before sailing away to Thessaly, to join with a second Pontic army that was approaching from the north.
With both Piraeus and Athens in his hands, Sulla was free to move north with most of his men to counter this new threat. His legate Curio was left to conduct the siege of the Acropolis. Aristion and his supporters held out for several weeks, before surrendering at about the same time as Archelaus was suffering defeat at the battle of Chaeronea. Aristion's supporters were executed as soon as Sulla returned to Athens, but Aristion survived for a little longer before being poisoned.
Those Athenians who survived the siege were not punished any further. The pro-Roman faction came back into power, and the citizens retained their liberties. Archelaus soon suffered a second defeat at Orchomenus, which effectively ended the Pontic invasion of Greece.