In the second year of the war, Athens suffered from a fearful visitation of the plague, which, however, made no way in the Peloponnese. It broke out also among the reinforcements dispatched to Potidæa; and it required all the skill of Pericles to reconcile the Athenians to the continuation of the war, after seeing their territories overrun for the second time for six weeks. By dint of dwelling on the supreme importance of their decisive command of the sea, and on the vast financial resources which secured their staying power, he maintained his ascendency until his death in the following year, though he had to submit to a fine. The events which followed his death only confirmed the profundity of his political judgment, and the accuracy with which he had gauged the capacities of the state. In that winter Potidæa was forced to capitulate to the Athenians. In the summer of the third year, the Lacedæmonians called on the Platæans to desert the Athenian alliance. On their refusal, Platæa was besieged by the allied forces of the Peloponnesians. With splendid resolution, the Platæans defeated the attempt of the allies to force an entry till they were able to complete and withdraw behind a second and more easily tenable line of defence, when the Peloponnesians settled down to a regular investment. The same year was marked by the brilliant operations of the Athenian admiral Phormio in the neighbourhood of Naupactus. On the other hand, a Peloponnesian squadron threatened the Piræus, caused some temporary panic, and awakened the Athenians to the necessity of maintaining a look-out, but otherwise effected little. The year is further noted for the invasion of Macedonia by the Thracian or Scythian king Sitalces, who was, however, induced to retire. In the next year, Lesbos revolted against the Athenian supremacy. As a result, an Athenian squadron blockaded Mitylene. The Lacedaæonians were well pleased to accept alliance with a sea-power which claimed to have struck against Athens, not as being subject to her, but in anticipation of attempted subjugation. The prompt equipment, however, of another Athenian fleet chilled the naval enthusiasm of Sparta. During this winter the Platæans began to feel in straits from shortage of supplies, and it was resolved that a party of them should break through the siege lines, and escape to Athens, a feat of arms which was brilliantly and successfully accomplished.