War was not yet formally declared when the Thebans attempted to seize Platæa, a town of Boeotia, which had long been closely allied to Athens. The attempt failed, and the Thebans were put to death; but the Platæans appealed to Athens for protection against their powerful neighbour, and when the Athenian garrison was sent to them, this was treated as a casus belli.
Preparations were urged on both sides; Sparta summoned her allies to muster their contingents on the Isthmus for the invasion of Attica, nearly all the mainland states joining the Peloponnesian league. The islanders and the cities in Asia Minor, on the other hand, were nearly all either actually subject to Athens or in alliance with her.
As Pericles advised, the Athenians left the country open to the ravages of the invading forces, and themselves retired within the city. In spite of the resentment of those who saw their property being laid waste, Pericles maintained his ascendency, and persuaded the people to devote their energies to sending out an irresistible fleet, and to establishing a great reserve both of ships and treasure, which were to be an annual charge and brought into active use only in the case of dire emergency. The fleet sailed round the Peloponnese, and the ravages it was able to inflict, with the alarm it created, caused the withdrawal of the forces in Attica.
In that winter Pericles delivered a great funeral oration, or panegyric, in memory of the Athenians who had so far fallen gloriously in defence of their country, in which he painted the characteristic virtues of the Athenian people in such a fashion as to rouse to the highest pitch the patriotic pride of his countrymen, and their confidence in themselves, in their future, and in their leader.
II.--Early Successes of Athens
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.