Phalanx
A phalanx (plural phalanges or phalanxes) is a rectangular array of infantry, typically spearmen, also called Hoplites, or later pikemen. The formation was typically close order, with the weapons of the first few lines (the exact number being dependant on their length) projecting forward and between the men in front, so that several layers of spearheads were arrayed between the enemy and the first line of men in the formation. The remaining men, those in the ranks that were too far back to reach the enemy, pointed their spears upwards, and were used as reserves when the men in front fell, and to provide 'push' to the entire formation so that the enemy was literally crushed under the advancing mass of spears.
The first phalanges appear on Sumerian inscriptions, and they dominate the battlefield for millennia, reaching their culmination in the Macedonian phalanx under Alexander the Great and his successors.
When made up of well trained soldiers, phalanges provide a very powerful forward defense, but have great difficulty advancing and staying in line. More importantly, because each spear is committed to the front and wedged in between the other men in the formation, they are vulnerable, and slow to present a defence, on the flanks.
Originally, the risk to the flank was negligible, because the standard tactic of the time was almost without exception little more than a simple frontal assault; cases of an army turning anothers flank seem to be more the result of accident than design. However, with the rise of more insightful battlefield commanders, and the emergence of cavalry and more manouverable forms of infantry such as the Roman legion, the shortcomings of the phalanx began to become too much of a liability and was gradually abandoned.
See also
Similar formations: