Quintus Curtius Rufus, History of Alexander 8.14.18

8.14.18

Phalanx quoque mediam Indorum aciem uno impetu perrupit. At Porus, qua equitem invehi senserat, beluas agi iussit: sed tardum et paene inmobile animal equorum velocitatem aequare non poterat. Ne sagittarum quidem ullus erat barbarie usus.

Their assistance is not of a kind to be depended on, and they may do their own side more damage than ours, for they are driven against the enemy by constraint, while terror turns them against their own ranks." Having spoken thus he was the first to put spurs to his horse. And now, as had been arranged, Coenus, upon seeing that Alexander was at close-quarters with the enemy, threw his cavalry with great fury upon their left wing. The phalanx besides, at the first onset, broke through the centre of the Indians. But Porus ordered his elephants to be driven into action where he had seen cavalry charging his ranks. The slow-footed unwieldy animals, however, were unfitted to cope with the rapid movements of horses, and the barbarians were besides unable to use even their arrows. These weapons were really so long and heavy that the archers could not readily adjust them on the string unless by first resting their bow upon the ground. Then, as the ground was slippery and hindered their efforts, the enemy had time to charge them before they could deliver their blows.