Meanwhile Cleomenes had returned to Sparta full of resentment against the Athenians, and resolved on punishing them, as well as on establishing his friend Isagoras as despot over them. Having been taught, however, by humiliating experience, that this was no easy achievement, he would not make the attempt, without having assembled a considerable force; he summoned allies from all the various states of the Peloponnesus, yet without venturing to inform them what he was about to undertake. He at the same time concerted measures with the Bœotians, and with the Chalcidians of Eubœa, for a simultaneous invasion of Attica on all sides. It appears that he had greater confidence in their hostile dispositions towards Athens than in those of the Peloponnesians; he was not afraid to acquaint them with his design, and probably the Bœotians were incensed with the recent interference of Athens in the affair of Platæa. As soon as these preparations were completed, the two kings of Sparta, Cleomenes and Demaratus, put themselves at the head of the united Peloponnesian force, marched into Attica, and advanced as far as Eleusis on the way to Athens. But when the allies came to know the purpose for which they were to be employed, a spirit of dissatisfaction manifested itself among them. They had no unfriendly sentiment towards Athens; and the Corinthians especially, favourably disposed rather than otherwise towards that city, resolved to proceed no further, withdrew their contingent from the camp, and returned home. At the same time, king Demaratus, either sharing in the general dissatisfaction, or moved by some grudge against his colleague which had not before manifested itself, renounced the undertaking also. And these two examples, operating upon the pre-existing sentiment of the allies generally, caused the whole camp to break up and return home without striking a blow.
We may here remark that this is the first instance known in which Sparta appears in act as recognised head of an obligatory Peloponnesian alliance, summoning contingents from the cities to be placed under the command of her king. Her headship, previously recognised in theory, passes now into act, but in an unsatisfactory manner, so as to prove the necessity of precaution and concert beforehand, which will be found not long wanting.
Pursuant to the scheme concerted, the Bœotians and Chalcidians attacked Attica at the same time that Cleomenes entered it. The former seized Œnoe and Hysiæ, the frontier demes of Attica on the side towards Platæa, while the latter assailed the northeastern frontier, which faces Eubœa. Invaded on three sides, the Athenians were in serious danger, and were compelled to concentrate all their forces at Eleusis against Cleomenes, leaving the Bœotians and Chalcidians unopposed. But the unexpected breaking up of the invading army from the Peloponnesus proved their rescue, and enabled them to turn the whole of their attention to the other frontier. They marched into Bœotia to the strait called Euripus, which separates it from Eubœa, intending to prevent the junction of the Bœotians and Chalcidians, and to attack the latter first apart. But the arrival of the Bœotians caused an alteration of their scheme; they attacked the Bœotians first, and gained a victory of the most complete character, killing a large number, and capturing seven hundred prisoners. On the very same day they crossed over to Eubœa, attacked the Chalcidians, and gained another victory so decisive that it at once terminated the war. Many Chalcidians were taken, as well as Bœotians, and conveyed in chains to Athens, where after a certain detention they were at last ransomed for two minæ per man; and the tenth of the sum thus raised was employed in the fabrication of a chariot and four horses in bronze, which was placed in the Acropolis to commemorate the victory. Herodotus saw this trophy when he was at Athens. He saw too, what was a still more speaking trophy, the actual chains in which the prisoners had been fettered, exhibiting in their appearance the damage undergone when the Acropolis was burnt by Xerxes: an inscription of four lines described the offerings and recorded the victory out of which they had sprung.