Plutarch Titus Flamininus 8

[1] Towards morning on the following day, after a mild and damp night, the clouds turned to mist, the whole plain was filled with profound darkness, a dense air came down from the heights into the space between the two camps, and as soon as day advanced all the ground was hidden from view. The parties sent out on either side for purposes of ambush and reconnaissance encountered one another in a very short time and went to fighting near what are called the Cynoscephalae, or Dog’s Heads. These are the sharp tops of hills lying close alongside one another, and got their name from a resemblance in their shape.

[2] As was natural on a field so difficult, there were alternations of flight and pursuit, each party sending out aid from their camps to those who from time to time were getting the worst of it and retreating, until at last, when the air cleared up and they could see what was going on, they engaged with all their forces. ¹
  With his right wing, then, Philip had the advantage, since from higher ground he threw his entire phalanx upon the Romans, who could not withstand the weight of its interlocked shields and the sharpness of its projecting pikes;

[3] but his left wing was broken up and scattered along the hills, and Titus, despairing of his defeated wing, rode swiftly along to the other, and with it fell upon the Macedonians. These were unable to hold their phalanx together and maintain the depth of its formation (which was the main source of their strength), being prevented by the roughness and irregularity of the ground, while for fighting man to man they had armour which was too cumbersome and heavy.

[4] For the phalanx is like an animal of invincible strength as long as it is one body and can keep its shields locked together in a single formation; but when it has been broken up into its parts, each of its fighting men loses also his individual force, as well because of the manner in which he is armed as because his strength lies in the mutual support of the parts of the whole body rather than in himself. This wing of the Macedonians being routed, some of the Romans pursued the fugitives, while others dashed out upon the flank of the enemy who were still fighting and cut them down, so that very soon their victorious wing also faced about, threw away their weapons, and fled.

[5] The result was that no fewer than eight thousand Macedonians were slain, and five thousand were taken prisoners. Philip, however, got safely away, and for this the Aetolians were to blame, who fell to sacking and plundering the enemy’s camp while the Romans were still pursuing, so that when the Romans came back to it they found nothing there.