He set himself first to extend and organize his own realm and to remodel his army. For a thousand years now the charging horse-chariot had been the decisive factor in battles, that and the close-fighting infantry. Mounted horsemen had also fought, but as a cloud of skirmishers, individually and without discipline. Philip made his infantry fight in a closely packed mass, the Macedonian phalanx, and he trained his mounted gentlemen, the knights or companions, to fight in formation and so invented cavalry. The master move in most of his battles and in the battles of his son Alexander was a cavalry charge. The phalanx _held_ the enemy infantry in front while the cavalry swept away the enemy horse on his wings and poured in on the flank and rear of his infantry. Chariots were disabled by bowmen, who shot the horses. With this new army Philip extended his frontiers through Thessaly to Greece; and the battle of Chæronia (338 B.C.), fought against Athens and her allies, put all Greece at his feet. At last the dream of Herodotus was bearing fruit. A congress of all the Greek states appointed Philip captain-general of the Græco- Macedonian confederacy against Persia, and in 336 B.C. his advanced guard crossed into Asia upon this long premeditated adventure. But he never followed it. He was assassinated; it is believed at the instigation of his queen Olympias, Alexander’s mother. She was jealous because Philip had married a second wife. BUST OF ALEXANDER THE GREAT BUST OF ALEXANDER THE GREAT _(As in the British Museum)_ But Philip had taken unusual pains with his son’s education. He had not only secured Aristotle, the greatest philosopher in the world, as this boy’s tutor, but he had shared his ideas with him and thrust military experience upon him. At Chæronia Alexander, who was then only eighteen years old, had been in command of the cavalry. And so it was possible for this young man, who was still only twenty years old at the time of his accession, to take up his father’s task at once and to proceed successfully with the Persian adventure.