The most remarkable improvement in the art of war was made by the Spartans, who, in addition to their strict military discipline, introduced the phalanx,—­files of picked soldiers, eight deep, heavily armed with spear, sword, and shield, placed in ranks of eight, at intervals of about six feet apart.  This phalanx of eight files and eight ranks,—­sixty-four men,—­closely locked when the soldiers received or advanced to attack, proved nearly impregnable and irresistible.  It combined solidity and the power of resistance with mobility.  The picked men were placed in the front and rear; for in skilful evolutions the front often became the rear, and the rear became the front.  Armed with spears projecting beyond the front, and with their shields locked together, the phalanx advanced to meet the enemy with regular step, and to the cadence of music; if beaten, it retired in perfect order.  After battle, each soldier was obliged to produce his shield as a proof that he had fought or retired as a soldier should.  The Athenian phalanx was less solid than that of Sparta,—­Miltiades having decreased the depth to four ranks, in order to lengthen his front,—­but was more efficient in a charge against the enemy.  The Spartan phalanx was stronger in defence, the Athenian more agile in attack.  The attack was nearly irresistible, as the soldiers advanced with accelerated motion, corresponding to the double-quick time of modern warfare.  This was first introduced by Miltiades at Marathon.

Philip of Macedon adopted the Spartan phalanx, but made it sixteen deep, which gave it greater solidity, and rendered it still more effective.  He introduced the large oval buckler and a larger and heavier spear.  When the phalanx was closed for action, each man occupied but three square feet of ground:  as the pikes were twenty-four feet in length, and projected eighteen feet beyond the front, the formation presented an array of points such as had never been seen before.  The greatest improvement effected by Philip, however, was the adoption of standing armies instead of the militia heretofore in use throughout the Grecian States.  He also attached great importance to his cavalry, which was composed of the flower of the nobility, about twelve hundred in number, all covered with defensive armor; these he formed into eight squadrons, and constituted them his body-guard.  The usual formation of the regular cavalry was in the form of a wedge, so as to penetrate and break the enemy’s line,—­a manoeuvre probably learned from Epaminondas of Thebes, a great master in the art of war, who defeated the Spartan phalanx by forming his columns upon a front less than their depth, thus enabling him to direct his whole force against a given point.  By these tactics he gained the great victory at Leuctra, as Napoleon likewise prevailed over the Austrians in his Italian campaign.  In like manner Philip’s son Alexander, following the example of Epaminondas, concentrated his forces upon the enemy’s centre,