But an act of treachery on the part of a native Greek rendered unavailing all the bravery of the keepers of the pass. A by-way leading over the mountains to the rear of the Spartans was revealed to Xerxes. The startling intelligence was brought to Leonidas that the Persians were descending the mountain-path in his rear. He saw instantly that all was lost. The allies were permitted to seek safety in flight while opportunity remained. But to him and his Spartan companions there could be no thought of retreat. Death in the pass, the defence of which had been intrusted to them, was all that Spartan honor and Spartan law now left them. The next day, surrounded by the Persian host, they fought with desperate valor; but, overwhelmed by mere numbers, they were slain to the last man. With them also perished seven hundred Thespians who had chosen death with their companions. Over the bodies of the Spartan soldiers a monument was afterwards erected with this inscription: "Stranger, tell the Lacedæmonians that we lie here in obedience to their orders." THE BURNING OF ATHENS.-Athens now lay open to the invaders. The Peloponnesians, thinking of their own safety simply, commenced throwing up defences across the isthmus of Corinth, working day and night under the impulse of an almost insane fear. Athens was thus left outside to care for herself. Counsels were divided. The Delphian oracle had obscurely declared, "When everything else in the land of Cecrops shall be taken, Zeus grants to Athena that the _wooden walls_ alone shall remain unconquered, to defend you and your children." The oracle was believed to be, as was declared, "firm as adamant." But there were various opinions as to what was meant by the "wooden walls." Some thought the Pythian priestess directed the Athenians to seek refuge in the forests on the mountains; but Themistocles (who it is thought may have himself prompted the oracle) contended that the ships were plainly indicated. The last interpretation was acted upon. All the soldiers of Attica were crowded upon the vessels of the fleet at Salamis. The aged men, with the women and children, were carried out of the country to different places of safety. All the towns of Attica, with the capital, were thus abandoned to the conquerors. A few days afterwards the Persians entered upon the deserted plain, which they rendered more desolate by ravaging the fields and burning the empty towns. Athens shared the common fate, and her splendid temples sank in flames. Sardis was avenged. The joy in distant Susa was unbounded.