Still, however, there was a possibility that the success which his own arms had failed to achieve might reward the exertions of his lieutenants.  Mardonius had expressed himself confident that with 300,000 picked soldiers he could overpower all resistance, and make Greece a satrapy of Persia.  Xerxes had raised his forces to that amount by sending Artabazus back from Sestos at the head of a corps d’armee numbering 40,000 men.  The whole army of 300,000 wintered in Thessaly; and Mardonius, when spring came, having vainly endeavored to detach the Athenians from the Grecian ranks, marched through Boeotia in Attica, and occupied Athens for the second time.  Hence he proceeded to menace the Peloponnese, where he formed an alliance with the Argives, who promised him that they would openly embrace the Persian cause.  At the same time the Athenians, finding that Sparta took no steps to help them, began to waver in their resistance, and to contemplate accepting the terms which Mardonius was still willing to grant them.  The fate of Greece trembled in the balance, and apparently was determined by the accident of a death and a succession, rather than by any wide-spread patriotic feeling or any settled course of policy.  Cleombrotus, regent for the young son of Leonidas, died, and his brother Pausanias—­a brave, clever, and ambitious man—­took his place.  We can scarcely be wrong in ascribing—­at least in part—­to this circumstance the unlooked-for change of policy, which electrified the despondent ambassadors of Athens almost as soon as Pausanias was installed in power.  It was suddenly announced that Sparta would take the offensive.  Ten thousand hoplites and 400,000 light-armed—­the largest army that she ever levied—­took the field, and, joined at the isthmus by above 25,000 Peloponnesians, and soon afterwards by almost as many Athenians and Megarians, proceeded to seek the foreigners, first in Attica, and then in the position to which they had retired in Boeotia.  On the skirts of Citheeron, near Platsea, a hundred and eight thousand Greeks confronted more than thrice their number of Persians and Persian subjects; and now at length the trial was to be made whether, in fair and open fight on land, Greece or Persia would be superior.  A suspicion of what the result would be might have been derived from Marathon.  But there the Persians had been taken at a disadvantage, when the cavalry, their most important arm, was absent.  Here the error of Datis was not likely to be repeated.  Mardonius had a numerous and well-armed cavalry, which he handled with no little skill.  It remained to be seen, when the general engagement came, whether, with both arms brought fully into play, the vanquished at Marathon would be the victors.