As long as Athens could keep the mastery of the sea, she would be able to defy the enemy. Famine would soon subdue her if she lost this mastery, for much of her corn supply came from abroad, and if the corn ships did not reach the Piraeus with their precious freight, the people would starve. On land Athens could not hope to hold her own against Sparta. Pericles knew this well, and so he urged the Athenians to place their trust in their ships. ‘Let us give up lands and houses,’ he said, ‘but keep a watch over the city and the sea. We should not, under any irritation at the loss of our property, give battle to the Peloponnesians, who far outnumber us. Mourn not for houses or lands, but for men; men may give these, but these will not give men. If I thought that you would listen to me, I would say to you, “Go yourselves and destroy them, and thereby prove to the Peloponnesians that none of these things move you.” Such is the power which the empire of the sea gives.’ The Peloponnesian War began in the early spring of 431 B.C. when the citizens of the little town of Thebes made a treacherous attack upon the town of Plataea. Thebes belonged to the Boeotian League, which was on good terms with Sparta, upon bad terms with Athens. Plataea was in alliance with Athens, but there were traitors among the citizens, and these determined to betray their city into the hands of the Thebans. One dark, stormy night the gates of the city were opened to admit a band of three hundred Thebans. The main body of the Theban force was still some distance off. At midnight the citizens of Plataea were awakened by the sound of trumpets. They dressed in haste, and then rushing to the market place found it in the hands of the Thebans, who were calling upon the citizens to forsake Athens and to join the Boeotian League. At first the Plataeans thought it would be useless to resist the enemy, but before long they found that there was only a small band of Thebans in the market place. Heavy rains had made the river Asopus rise, and the main body of the enemy was still on the farther side of the river, looking in vain for a ford. So the Plataeans shut their gates, barricaded their streets with wagons, and then boldly attacked the enemy. The Thebans were soon separated from one another and lost their way in the unknown and dusky streets. To add to their confusion, from windows and roofs, heavy missiles were hurled down upon them by the angry Plataean women. A few scaled the city wall and escaped, but the greater number, rushing through a large door which they mistook for one of the city gates, found themselves in a granary from which there was no escape save by the door through which they had entered. It was already held by the Plataeans, and the Thebans were taken prisoners and commanded to lay down their arms.