War was now fairly kindled. All Greece looked on in suspense as its two leading cities were about to engage in a strife of which no man could forsee the end; but the youth, with which both Athens and Peloponnesus then abounded, having had no experience of the bitter calamities of war, rushed into it with ardour. It was a war of principles and races. Athens was a champion of democracy, Sparta of aristocracy; Athens represented the Ionic tribes, Sparta the Dorian; the former were fond of novelty, the latter were conservative and stationary; Athens had the command of the sea, Sparta was stronger upon land. On the side of Sparta was ranged the whole of Peloponnesus, except Argos and Achaia, together with the Megarians, Boeotians, Phocians, Opuntian Locrians, Ambraciots, Leucadians, and Anactorians. The allies of Athens, with the exception of the Thessalians, Acarnanians, Messenians at Naupactus, and Plataeans, were all insular, and consisted of the Chians, Lesbians, Corcyraeans, and Zacynthians, and shortly afterwards of the Cephallenians, To these must be added her tributary towns on the coast of Thrace and Asia Minor, together with all the islands north of Crete, except Melos and Thera.

The Peloponnesians commenced the war by an invasion of Attica, with a large army, under the command of the Spartan King Archidamus (B.C. 431). Pericles had instructed the inhabitants of Attica to secure themselves and their property within the walls of Athens. They obeyed his injunctions with reluctance, for the Attic population had from the earliest times been strongly attached to a rural life. But the circumstances admitted of no alternative. Archidamus advanced as far as Acharnae, a flourishing Attic borough situated only about seven miles from Athens. Here he encamped on a rising ground within sight of the metropolis, and began to lay waste the country around, expecting probably by that means to provoke the Athenians to battle. But in this he was disappointed. Notwithstanding the murmurs and clamours of the citizens Pericles remained firm, and steadily refused to venture an engagement in the open held. The Peloponnesians retired from Attica after still further ravaging the country; and the Athenians retaliated by making descents upon various parts of the coasts of Peloponnesus, and ravaging the territory of Megara.

Such were the results of the first campaign. From the method in which the war was conducted it had become pretty evident that it would prove of long duration; and the Athenians now proceeded to provide for this contingency. It was agreed that a reserve fund of 1000 talents should be set apart, which was not to be touched in any other case than an attack upon Athens by sea. Any citizen who proposed to make a different use of the fund incurred thereby the punishment of death. With the same view it was resolved to reserve every year 100 of their best triremes, fully manned and equipped.

Towards the winter Pericles delivered, from a lofty platform erected in the Ceramicus, the funeral oration of those who had fallen in the war. This speech, or at all events the substance of it, has been preserved by Thucydides, who may possibly have heard it pronounced. It is a valuable monument of eloquence and patriotism, and particularly interesting for the sketch which it contains of Athenian manners as well as of the Athenian constitution.

In the following year (B.C. 430) the Peloponnesians, under Archidamus, renewed their invasion of Attica. At the same time the Athenians were attacked by a more insidious and a more formidable enemy. The plague broke out in the crowded city. This terrible disorder, which was supposed to have originated in AEthiopia, had already desolated Asia and many of the countries around the Mediterranean. A great proportion of those who were seized perished in from seven to nine days. It frequently attacked the mental faculties, and left even those who recovered from it so entirely deprived of memory that they could recognise neither themselves nor others. The disorder being new, the physicians could find no remedy in the resources of their art. Despair now began to take possession of the Athenians. Some suspected that the Peloponnesians had poisoned the wells; others attributed the pestilence to the anger of Apollo. A dreadful state of moral dissolution followed. The sick were seized with unconquerable despondency; whilst a great part of the population who had hitherto escaped the disorder, expecting soon to be attacked in turn, abandoned themselves to all manner of excess, debauchery, and crime. The numbers carried off by the pestilence can hardly be estimated at less than a fourth of the whole population,