History of the Peloponnesian War

After this the conflict commenced: the Argives and their allies advancing with haste and impetuosity; the Lacedaemonians slowly, and to the music of many flute-players, placed amongst them according to custom, not with a religious object, but that they might advance evenly, stepping in time, and so that their line might not be broken, a thing which large armies are apt to do in their approaches to an enemy.

While they were yet closing in battle, King Agis resolved to execute a manoeuvre, as follows. All armies, on going into battle, are forced out too much on their right wing; because the men, in their fear, each shelter, as far as possible, their exposed side with the shield of the man who is posted next to them on the right, and think that the closer they are locked together, the more effectually they are protected. The man who primarily gives occasion to this is he who stands first on the right wing, through wishing continually to withdraw from the enemy his own unarmed side; and the rest follow him under the influence of the same fear.