The gates were opened to them by a Plataean called Naucleides, who, with his party, had invited them in, meaning to put to death the citizens of the opposite party, bring over the city to Thebes, and thus obtain power for themselves.

This was arranged through Eurymachus, son of Leontiades, a person of great influence at Thebes. For Plataea had always been at variance with Thebes; and the latter, foreseeing that war was at hand, wished to surprise her old enemy in time of peace, before hostilities had actually broken out. Indeed this was how they got in so easily without being observed, as no guard had been posted.

After the soldiers had grounded arms in the marketplace, those who had invited them in wished them to set to work at once and go to their enemies' houses. This, however, the Thebans refused to do, but determined to make a conciliatory proclamation, and if possible to come to a friendly understanding with the citizens. Their herald accordingly invited any who wished to resume their old place in the confederacy of their countrymen to ground arms with them, for they thought that in this way the city would readily join them.

On becoming aware of the presence of the Thebans within their gates, and of the sudden occupation of the town, the Plataeans concluded in their alarm that more had entered than was really the case, the night preventing their seeing them. They accordingly came to terms, and accepting the proposal, made no movement; especially as the Thebans offered none of them any violence.