国立情報学研究所 - ディジタル・シルクロード・プロジェクト
『東洋文庫所蔵』貴重書デジタルアーカイブ

the cavalry first landed moved forward. 'Owing, however, to ignorance of the
locality he had unawares landed not on the mainland, but upon an island and
that a great one . . . separated from the mainland by a branch of the river in
which the water was shallow; but the violent storm of rain which had lasted
most of the night, had so swollen the stream that the horsemen could not find
the ford. . . . When at last the ford was found, he led his men through it with
difficulty; for the water where deepest reached higher than the breast of the
foot-soldiers, and as for the horses their heads only were above the river.'¹⁵

We need not follow the details of the events subsequent to the crossing, as
recorded by Arrian mainly from the account of Ptolemy, son of Lagos and future
king of Egypt, who shared Alexander's bold enterprise; a brief summary will
suffice, including such points as may have a topographical bearing. Alexander,
leading forward his cavalry, some 5,000 strong, had no difficulty in routing the
inferior force of horsemen and chariots which Poros had first sent ahead under
his own son. The chariots proved useless in the action, having stuck in the clay,
and were all captured. On learning of this rout and of Alexander himself having
crossed with the strongest division of the Macedonians, Poros decided to leave
only a small force in camp to watch Krateros and to march against Alexander
with all his remaining host. He is said to have taken 'all his cavalry, 4,000
strong, all his chariots, 300 in number, 200 of his elephants, and 30,000 efficient
infantry'.¹⁶

About the order of battle adopted by Poros, Arrian gives us details which, as
we shall see, afford a useful topographical indication. 'When he found a place
where he saw there was no clay, but that the ground from its sandy nature was
all flat and firm, and suited for the movements of cavalry whether charging or
falling back, he then drew up his army in order of battle, posting his elephants
in the front line at intervals of at least a plethron (101 feet), so as to have his
elephants ranged in front before the whole of his infantry, and so to spread terror
at all points among Alexander's cavalry. . . . Behind these he drew up his in-
fantry, which did not close up in one line with the elephants, but formed a second
line in their rear so that only bands (λόχοι) were inserted in the intervals. He
had also infantry posted on the wings beyond the elephants. On both sides of the
infantry the cavalry had been drawn up, and in front of it the chariots.'¹⁷ There
is nothing stated that could suggest that this very extensive line of battle was
protected on its flanks by any physical feature such as the river bank or broken
ground. This point deserves to be specially noted as it has its bearing on the
tactical development of the battle, and on account of the light which this throws
on the topography of the ground where it was fought.