Thucydides, History of the Peloponnesian War
Benjamin Jowett, Ed.

18. The Lacedaemonians also prepared for their already projected invasion of Attica¹. They² were kept to their purpose by the Syracusans and Corinthians, who, having heard of the reinforcements which the Athenians were sending to Sicily, hoped they might be stopped by the invasion, Alcibiades was always at hand insisting upon the importance of fortifying Decelea and of carrying on the war with vigour. [2] Above all, the Lacedaemonians were inspirited by the thought that the Athenians would be more easily overthrown now that they had two wars on hand, one against themselves, and another against the Sicilians. They considered also that this time they had been the first offenders against the treaty, whereas in the former war the transgression had rather been on their own side. For the Thebans had entered Plataea in time of peace³, and they themselves had refused arbitration when offered by the Athenians, although the former treaty forbade war in case an adversary was willing to submit to arbitration⁴. They felt that their ill success was deserved, and they took seriously to heart the disasters which had befallen them at Pylos and elsewhere. [3] But now the Athenians with a fleet of thirty ships had gone forth from Argive territory and ravaged part of the lands of Epidaurus and Prasiae, besides other places⁵; marauding expeditions from Pylos were always going on; and whenever quarrels arose about disputed points in the treaty and the Lacedaemonians proposed arbitration, the Athenians refused it. Reflecting upon all this, the Lacedaemonians concluded that the guilt of their former transgression was now shifted to the Athenians, and they were full of warlike zeal. [4] During the winter they bade their allies provide iron, and themselves got tools in readiness for the fortification of Decelea. They also prepared, and continually urged the other Peloponnesians to prepare, the succours which they intended to send in merchant-vessels to the Syracusans. And so the winter ended, and with it the eighteenth year in the Peloponnesian War of which Thucydides wrote the history.