Nothing remained for the Lacedæmonians but to march into Bœotia, where their presence was welcome to Thebes. They entered the valley of the Asopus, and encamped in the territory of Tanagra, not far from the frontiers of Attica. Without calculating the consequences, the Athenians had brought themselves into an extremely dangerous situation. … Their difficulties increased when, contemporaneously, evil signs of treasonable plots made their appearance in the interior of the city. … See ATHENS: B. C. 460-449. Thus, then, it was now necessary to contend simultaneously against foes within and foes without, to defend the constitution as well as the independence of the state. Nor was the question merely as to an isolated attack and a transitory danger; for the conduct of the Spartans in Bœotia clearly showed that it was now their intention to restore to power Thebes … because they were anxious to have in the rear of Athens a state able to stop the extension of the Attic power in Central Greece. This intention could be best fulfilled by supporting Thebes in the subjugation of the other Bœotian cities. For this purpose the Peloponnesians had busily strengthened the Theban, i. e. the oligarchical party, in the whole of the country, and encircled Thebes itself with new fortifications. Thebes was from a country town to become a great city, an independent fortified position, and a base for the Peloponnesian cause in Central Greece. Hence Athens could not have found herself threatened by a more dangerous complication. The whole civic army accordingly took the field, amounting, together with the Argives, and other allies, to 14,000 men, besides a body of Thessalian cavalry. In the low ground by the Asopus below Tanagra the armies met. An arduous and sanguinary struggle ensued, in which for the first time Athens and Sparta mutually tested their powers in a regular battle. For a long time the result was doubtful; till in the very thick of the battle the cavalry went over to the enemy, probably at the instigation of the Laconian party. This act of treason decided the day in favor of Sparta, although patriotic Athenians would never consent to count this among the battles lost by Athens. The Spartans were far from fulfilling the expectations of the party of the Oligarchs. As soon as they knew that the passes of the Isthmus were once more open, they took their departure, towards the fall of the year, through Megara, making this little country suffer for its defection by the devastation of its territory. … They reckoned upon Thebes being for the present strong enough to maintain herself against her neighbors; for ulterior offensive operations against Athens, Tanagra was to serve as a base. The plan was good, and the conjuncture of affairs favorable. But whatever the Spartans did, they did only by halves: they concluded a