Pasimelus and Alcimenes took the lead in this enterprise. They obtained a secret interview with Praxitas, the Spartan commander at Sicyon, and proposed to admit him and his troops within the walls that joined Corinth with Lechæum, her port on the western gulf. He knew the men, and embraced their offer; and at an appointed hour of night came with a mora of Lacedæmonians, and a body of Sicyonians and of Corinthian exiles, to a gate where the conspirators had contrived to get themselves placed on duty. He was introduced without any opposition; but as the space between the walls was large, and he had brought but a small force with him, he threw up a slight entrenchment, to secure himself until the succours which he expected should arrive. During the next day he remained quiet, and was not attacked; though, besides the garrison of the city, there was a body of Bœotians behind him at Lechæum. But aid had been summoned from Argos, and on the day following the Argive forces arrived, and, confident in their numbers, immediately sought the enemy. They were supported by their Corinthian partisans, and by a body of mercenaries commanded by Iphicrates, an Athenian general, who in this war laid the foundation of his military renown.
The superiority of the Lacedæmonian troops over the other Greeks, and the terror they inspired even when they were greatly outnumbered, was again strikingly manifested in the engagement which ensued. The Argives forced their way through the entrenchment, and drove the handful of Sicyonians before them down to the sea. But when the Lacedæmonians came up, they took to flight, without offering any resistance, and made for the city. But, meeting with the Corinthian exiles, who had defeated the mercenaries, and were returning from the pursuit, they were driven back, and those who did not make their escape by ladders over the wall, were slaughtered by the Lacedæmonians like a flock of sheep. Lachæum was taken, and the Bœotian garrison was put to the sword. After his victory Praxitas was joined by the expected contingents of the allies, and he made use of them first to demolish the Long Walls, for a space sufficient to afford a passage for an army. Next, crossing the isthmus, he took and garrisoned the towns of Sidus and Crommyon. On his return he fortified the heights of Epieicea, which commanded one of the most important passes, and then disbanded his army, and returned to Sparta.
Two important consequences of the long series of hostilities in which all the Greek states had been engaged now became apparent. The number of persons who were thrown upon war as a means of subsistence had so much increased, that the contending powers were able to carry on the struggle with mercenary troops. Another result of the long practice of war was, that it had begun to be more and more studied as an art, and cultivated with new refinements.
Thus Iphicrates had been led to devote his attention to the improvement of a branch of the light infantry, which had hitherto been accounted of little moment in the Greek military system. He had formed a new body of targeteers, which in some degree combined the peculiar advantages of the heavy and light troops, and was equally adapted for combat and pursuit. To attain these objects, he had substituted a linen corslet for the ancient coat of mail, and had reduced the size of the shield, while he doubled the length of the spear and the sword. At the head of this corps he made frequent inroads into Peloponnesus, and in the territory of Phlius he surprised the forces of the little state in an ambuscade, and made so great a slaughter of them that the Phliasians were obliged to admit a Lacedæmonian garrison into their town. But in Arcadia such was the terror inspired by the troops of Iphicrates, that they were suffered to plunder the country with impunity, and the Arcadians did not venture to meet them in the field. On the other hand they were themselves no less in dread of the Lacedæmonians, who had taught them to keep aloof in a manner which proved the peculiar excellence of the Spartan military training.