XIII. While the cause of Greece was thus trembling in the balance, and Athens was especially in danger, certain Athenians of noble birth, who had lost their former wealth during the war, and with it their influence in the city, being unable to bear to see others exalted at their expense, met in secret in a house in Platæa and entered into a plot to overturn the free constitution of Athens. If they could not succeed in this, they pledged themselves to ruin, the city and betray it to the Persians. While these men were plotting in the camp, and bringing many over to their side, Aristeides discovered the whole conspiracy. Afraid at such a crisis to take any decisive step, he determined, while carefully watching the conspirators, yet not at once to seize them all, not knowing how far he might have to proceed if he acted according to strict justice. From all the conspirators he arrested eight. Two of these, who would have been the first to be put on their trial, Æschines of Lampra, and Agesias of Acharna, made their escape out of the camp, and Aristeides pardoned the others, as he wished to give an opportunity to those who believed themselves unsuspected, to take courage and repent. He also hinted to them that the war afforded them a means of clearing themselves from any suspicion of disloyalty by fighting for their country like good men and true. XIV. After this, Mardonius made trial of Grecian courage, by sending the whole of his cavalry, in which he was much the stronger, to attack them where they were, all except the Megarians, encamped at the foot of Mount Kithæron, in an easily-defended rocky country. These men, three thousand in number, were encamped nearer the plain, and suffered much from the attacks of the horsemen, who surrounded them on all sides. They sent a messenger in great haste to Pausanias, begging him to send assistance, as they could not by themselves resist the great numbers of the barbarians. Pausanias, hearing this, and seeing the camp of the Megarians overwhelmed with darts and arrows, while the defenders were huddled together in a narrow compass, knew not what to do. He did not venture to attack cavalry with the heavy-armed Lacedæmonian infantry, but offered it as an opportunity for winning praise and honour, to the generals who were with him, that they should volunteer to go to help the Megarians in their extremity. All hesitated, but Aristeides claimed the honour for the Athenians, and sent the bravest of his captains, Olympiodorus, with three hundred picked men, besides some archers. As they quickly got into array and charged at a run, Masistius, the leader of the enemy, a man of great bodily strength and beauty, seeing them, wheeled round his horse, and rode to attack them. They sustained his attack and closed with his horsemen, and a sharp struggle took place, both parties fighting as though the issue of the war depended on their exertions. The horse of Masistius was at length wounded by an arrow and threw his rider.