Hippias supposed that the dream had in this way come true. As the Athenians were marshalled in the precinct of Heracles, the Plataeans came to help them in full force. The Plataeans had put themselves under the protection of the Athenians,In 519, according to Thucydides (Thuc. 3.68); Grote gives a later date. and the Athenians had undergone many labors on their behalf. This is how they did it:

when the Plataeans were pressed by the Thebans, they first tried to put themselves under the protection of Cleomenes son of Anaxandrides and the Lacedaemonians, who happened to be there. But they did not accept them, saying, “We live too far away, and our help would be cold comfort to you. You could be enslaved many times over before any of us heard about it.

We advise you to put yourselves under the protection of the Athenians, since they are your neighbors and not bad men at giving help.” The Lacedaemonians gave this advice not so much out of goodwill toward the Plataeans as wishing to cause trouble for the Athenians with the Boeotians.

So the Lacedaemonians gave this advice to the Plataeans, who did not disobey it. When the Athenians were making sacrifices to the twelve gods,The twelve gods were Zeus, Hera, Poseidon, Demeter, Apollo, Artemis, Hephaestus, Athena, Ares, Aphrodite, Hermes, Hestia. The bwmo\s was a central altar in the agora, from which distances were reckoned. they sat at the altar as suppliants and put themselves under protection. When the Thebans heard this, they marched against the Plataeans, but the Athenians came to their aid.

As they were about to join battle, the Corinthians, who happened to be there, prevented them and brought about a reconciliation. Since both sides desired them to arbitrate, they fixed the boundaries of the country on condition that the Thebans leave alone those Boeotians who were unwilling to be enrolled as Boeotian. After rendering this decision, the Corinthians departed. The Boeotians attacked the Athenians as they were leaving but were defeated in battle.

The Athenians went beyond the boundaries the Corinthians had made for the Plataeans, fixing the Asopus river as the boundary for the Thebans in the direction of Plataea [23.2667,38.2] (Perseus) Plataea and Hysiae. So the Plataeans had put themselves under the protection of the Athenians in the aforesaid manner, and now came to help at Marathon.