The great battle of all that was fought with Darius, was not, as most writers tell us, at Arbela, but at Gaugamela, which, in their language, signifies the camel's house, forasmuch as one of their ancient kings having escaped the pursuit of his enemies on a swift camel, in gratitude to his beast settled him at this place, with an allowance of certain villages and rents for his maintenance. It came to pass that in the month Boedromion, about the beginning of the Feast of Mysteries at Athens, there was an eclipse of the moon, the eleventh night after which, the two armies being now in view of one another, Darius kept his men in arms, and by torchlight took a general review of them. But Alexander, while his soldiers slept, spent the night before his tent with his diviner Aristander, performing certain mysterious ceremonies, and sacrificing to the god Fear.

In the meanwhile the oldest of his commanders, and chiefly Parmenio, when they beheld all the plain between Niphates and the Gordyaean mountains shining with the lights and fires which were made by the barbarians, and heard the uncertain and confused sound of voices out of their camp, like the distant roaring of a vast ocean, were so amazed at the thoughts of such a multitude, that after some conference among themselves, they concluded it an enterprise too difficult and hazardous for them to engage so numerous an enemy in the day, and therefore meeting the king as he came from sacrificing, besought him to attack Darius by night, that the darkness might conceal the danger of the ensuing battle. To this he gave them the celebrated answer, "I will not steal a victory," which, though some at the time thought it a boyish and inconsiderate speech, as if he played with danger, others regarded as an evidence that the confided in his present condition, and acted on a true judgment of the future, not wishing to leave Darius, in case he were worsted, the pretext of trying his fortune again, which he might suppose himself to have, if he could impute his overthrow to the disadvantage of the night, as he did before to the mountains, the narrow passages, and the sea. For while he had such numerous forces and large dominions still remaining, it was not any want of men or arms that could induce him to give up the war, but only the loss of all courage and hope upon the conviction of an undeniable and manifest defeat.

After they were gone from him with this answer, he laid himself down in his tent and slept the rest of the night more soundly than was usual with him, to the astonishment of the commanders. Not only before the battle, but in the height of the danger, he showed himself great, and manifested the self-possession of a just foresight and confidence. For the battle for some time fluctuated and was dubious. The left wing, where Parmenio commanded, was so impetuously charged by the Bactrian horse that it was disordered and forced to give ground, at the same time that Mazaeus had sent a detachment around to fall upon those who guarded the baggage, which so disturbed Parmenio, that he sent messengers to acquaint Alexander that the camp and baggage would be all lost unless he immediately relieved the rear by a considerable reinforcement drawn out of the front. This message being brought him just as he was giving the signal to those about him for the onset, he bade them tell Parmenio that he must have surely lost the use of his reason, and had forgotten, in his alarm, that soldiers, if victorious, become masters of their enemies' baggage; and if defeated, instead of taking care of their wealth or their slaves, have nothing more to do but to fight gallantly and die with honor. When he had said this, he put on his helmet, having the rest of his arms on before he came out of his tent, which were a coat of the Sicilian make, girt close about him, and over that a breastpiece of thickly quilted linen, which was taken among other booty at the battle of Issus. The helmet, which was made by Theophilus, though of iron, was so well wrought and polished, that it was as bright as the most refined silver. To this was fitted a gorget of the same metal, set with precious stones His sword, which was the weapon he most used in fight, was given him by the king of the Citieans, and was of an admirable temper and lightness. The belt which he also wore in all engagements, was of much richer workmanship than the rest of his armor. It was the work of the ancient Helicon, and had been presented to him by the Rhodians, as a mark of their respect to him. So long as he was engaged in drawing up his men, or riding about to give orders or directions, or to view them, he spared Bucephalas, who was now growing old, and made use of another horse; but when he was actually to fight, he sent for him again, and as soon as he was mounted, commenced the attack.

He made the longest address that day to the Thessalians and other Greeks, who answered him with loud shouts desiring him to lead them on against the barbarians, upon which he shifted his javelin into his left hand, and with his right lifted up towards heaven, besought the gods, as Callisthenes tells us, that if he was of a truth the son of Jupiter, they would be pleased to assist and strengthen the Grecians. At the same time the augur Aristander, who had a white mantle about him, and a crown of gold on his head, rode by and showed them an eagle that soared just over Alexander, and directed his flight towards the enemy; which so animated the beholders, that after mutual encouragements and exhortations, the cavalry charged at full speed, and were followed in a mass by the whole phalanx of the foot. But before they could well come to blows with the first ranks, the barbarians shrunk back, and were hotly pursued by Alexander, who drove those that fled before him into the middle of the battle, where Darius himself was in person, whom he saw from a distance over the foremost ranks, conspicuous in the midst of his lifeguard, a tall and fine-looking man, drawn in a lofty chariot, defended by an abundance of the best cavalry who stood close in order about it, ready to receive the enemy. But Alexander's approach was so terrible, forcing those who gave back upon those who yet maintained their ground, that he beat down and dispersed them almost all. Only a few of the bravest and valiantest opposed the pursuit, who were slain in their king's presence, falling in heaps upon one another, and in the very pangs of death striving to catch hold of the horses. Darius now seeing all was lost, that those who were placed in front to defend him were broken and beaten back upon him, that he could not turn or disengage his chariot without great difficulty, the wheels being clogged and entangled among the dead bodies, which lay in such heaps as not only stopped, but almost covered the horses, and made them rear and grow so unruly, that the frighted charioteer could govern them no longer, in this extremity was glad to quit his chariot and his arms, and mounting, it is said, upon a mare that had been taken from her foal, betook himself to flight.

This battle being thus over, seemed to put a period to the Persian empire; and Alexander, who was now proclaimed king of Asia, returned thanks to the gods in magnificent sacrifices, and rewarded his friends and followers with great sums of money, and places, and governments of provinces.

From here he marched through the province of Babylon, which immediately submitted to him, and was much surprised at the sight in one place where fire issues in a continuous stream, like a spring of water, out of a cleft in the earth, and the stream of naphtha, which, not far from this spot, flows out so abundantly as to form a sort of lake. This naphtha, in other respects resembling bitumen, is so subject to take fire, that before it touches the flame, it will kindle at the very light that surrounds it, and often inflame the intermediate air also. The barbarians, to show the power and nature of it, sprinkled the street that led to the king's lodgings with little drops of it, and when it was almost night, stood at the further end with torches, which being applied to the moistened places, the first at once taking fire, instantly, as quick as a man could think of it, it caught from one end to another, in such a manner that the whole street was one continuous flame.

Alexander, in his own letters, has given us an account of his war with Porus. He says that two armies were separated by the river Hydaspes, on whose opposite bank Porus continually kept his elephants in order of battle, with their heads towards their enemies, to guard the passage; that he, on the other hand, made every day a great noise and clamor in his camp, to dissipate the apprehensions of the barbarians; that one stormy, dark night he passed the river, at a distance from the place where the enemy lay, into a little island, with part of his foot, and the best of his horse. Here there fell a most violent storm of rain accompanied with lightning and whirlwinds, and although he saw some of his men burnt and dying with the lightning, he nevertheless quitted the island and made over to the other side. Here, apprehending the multitude of the enemy, and to avoid the shock of their elephants, he divided his forces, and attacked their left wing himself, commanding Coenus to fall upon the right, which was performed with good success. By this means both wings being broken, the enemies fell back in their retreat upon the centre, and crowded in upon their elephants. There rallying, they fought a hand to hand battle, and it was the eighth hour of the day before they were entirely defeated.

Almost all the historians agree in relating that Porus was four cubits and a span high, and that when he was upon his elephant, which was of the largest size, his stature and bulk were so answerable, that he appeared to be proportionably mounted, as a horseman on his horse. This elephant, during the whole battle, gave many singular proofs of sagacity and of particular care of the king, whom as long as he was strong and in a condition to fight, he defended with great courage, repelling those who set upon him; and as soon as he perceived him overpowered with his numerous wounds and the multitude of darts that were thrown at him, to prevent his falling off, he softly knelt down and began to draw out the darts with his proboscis. When Porus was taken prisoner, and Alexander asked him how he expected to be used, he answered, "As a king." And Alexander, accordingly, not only suffered him to govern his own kingdom as satrap under himself, but gave him also the additional territory of various independent tribes whom he subdued.

Some little time after the battle with Porus, Bucephalas died, as most of the authorities state, under cure of his wounds, or as Onesicritus says, of fatigue and age, being thirty years old. Alexander was no less concerned at his death, than if he had lost an old companion or an intimate friend, and built a city, which he named Bucephalia, in memory of him, on the bank of the river Hydaspes.

Aristobulus tells us that Alexander died of a raging fever, having, in a violent thirst, taken a copious draught of wine, upon which he fell into delirium, and died on the thirtieth day of the month Daesius.