The territories of the Spartan alliance reached as far north as Megara, which served as a base to move to Athens. More to the north, beyond the Cithaeron mountains, was Plataea, situated halfway between Megara and Thebes, another ally of Sparta. The enemies of Athens needed Plataea if they wanted to support each other. In the spring of 431, the Thebans had tried a sneak attack (more...) but it had been foiled; in 429, the Spartan king Archidamus II laid siege to Plataea.
The Athenian historian Thucydides (c.460-c.395) describes the siege and mentions many interesting details about ancient warfare. The town was bravely defended but eventually fell in 427; all defenders were killed after a mock trial.
The translation of Thucydides, History of the Peloponnesian War 2.75-78 was made by Richard Crawley. A satellite photo of the town can be found here.
The siege of Plataea
[2.75.1] After an appeal to the gods Archidamus put his army in motion. First he enclosed the town with a palisade formed of the fruit trees which they cut down, to prevent further egress from Plataea; next they threw up a mound against the city, hoping that the largeness of the force employed would ensure the speedy reduction of the place.
[2.75.2] They accordingly cut down timber from Mount Cithaeron, and built it up on either side, laying it like lattice-work to serve as a wall to keep the mound from spreading abroad, and carried to it wood and stones and earth and whatever other material might help to complete it.
[2.75.3] They continued to work at the mound for seventy days and nights without intermission, being divided into relief parties to allow of some being employed in carrying while others took sleep and refreshment; the Spartan officer attached to each contingent keeping the men to the work.
[2.75.4] But the Plataeans, observing the progress of the mound, constructed a wall of wood and fixed it upon that part of the city wall against which the mound was being erected, and built up bricks inside it which they took from the neighboring houses.
[2.75.5] The timbers served to bind the building together, and to prevent its becoming weak as it advanced in height; it had also a covering of skins and hides, which protected the woodwork against the attacks of burning missiles and allowed the men to work in safety. Thus the wall was raised to a great height, and the mound opposite made no less rapid progress. The Plataeans also thought of another expedient; they pulled out part of the wall upon which the mound abutted, and carried the earth into the city.
[2.76.1] Discovering this, the Peloponnesians twisted up clay in wattles of reed and threw it into the breach formed in the mound, in order to give it consistency and prevent its being carried away like the soil. Stopped in this way, the Plataeans changed their mode of operation, and digging a mine from the town calculated their way under the mound, and began to carry off its material as before.
[2.76.2] This went on for a long while without the enemy outside finding it out, so that for all they threw on the top their mound made no progress in proportion, being carried away from beneath and constantly settling down in the vacuum.
[2.76.3] But the Plataeans, fearing that even thus they might not be able to hold out against the superior numbers of the enemy, had yet another invention. They stopped working at the large building in front of the mound, and starting at either end of it inside from the old low wall, built a new one in the form of a crescentnote[The technical term is demilune.] running in towards the town; in order that in the event of the great wall being taken this might remain, and the enemy have to throw up a fresh mound against it, and as they advanced within might not only have their trouble over again, but also be exposed to missiles on their flanks.
[2.76.4] While raising the mound the Peloponnesians also brought up engines against the city, one of which was brought up upon the mound against the great building and shook down a good piece of it, to the no small alarm of the Plataeans. Others were advanced against different parts of the wall but were lassoed and broken by the Plataeans; who also hung up great beams by long iron chains from either extremity of two poles laid on the wall and projecting over it, and drew them up at an angle whenever any point was threatened by the engine, and loosing their hold let the beam go with its chains slack, so that it fell with a run and snapped off the nose of the battering ram.
[2.77.1] After this the Peloponnesians, finding that their engines effected nothing, and that their mound was met by the counterwork, concluded that their present means of offense were unequal to the taking of the city, and prepared for its circumvallation.
[2.77.2] First, however, they determined to try the effects of fire and see whether they could not, with the help of a wind, burn the town, as it was not a large one; indeed they thought of every possible expedient by which the place might be reduced without the expense of a blockade.
[2.77.3] They accordingly brought faggots of brushwood and threw them from the mound, first into the space between it and the wall; and this soon becoming full from the number of hands at work, they next heaped the faggots up as far into the town as they could reach from the top,
[2.77.4] and then lighted the wood by setting fire to it with sulfur and pitch. The consequence was a fire greater than any one had ever yet seen produced by human agency, though it could not of course be compared to the spontaneous conflagrations sometimes known to occur through the wind rubbing the branches of a mountain forest together.
[2.77.5] And this fire was not only remarkable for its magnitude, but was also, at the end of so many perils, within an ace of proving fatal to the Plataeans; a great part of the town became entirely inaccessible, and had a wind blown upon it, in accordance with the hopes of the enemy, nothing could have saved them.
[2.77.6] As it was, there is also a story of heavy rain and thunder having come on by which the fire was put out and the danger averted.
[2.78.1] Failing in this last attempt, the Peloponnesians left a portion of their forces on the spot, dismissing the rest, and built a wall of circumvallation round the town, dividing the ground among the various cities present; a ditch being made within and without the lines, from which they got their bricks.
[2.78.2] All being finished by about the rising of Arcturus,note[About 20 September 429.] they left men enough to man half the wall, the rest being manned by the Boeotians, and drawing off their army dispersed to their several cities.
[2.78.3] The Plataeans had before sent off their wives and children and oldest men and the mass of the non-combatants to Athens; so that the number of the besieged left in the place comprised 400 of their own citizens, 80 Athenians, and 110 women to bake their bread. This was the sum total at the commencement of the siege, and there was no one else within the walls, bond or free. Such were the arrangements made for the blockade of Plataea.