Titus Livius (Livy), The History of Rome, Book 37
Evan T. Sage, PhD professor of latin and head of the department of classics in the University of Pittsburgh, Ed.

¹ The Romans held the centre, the Latins the flanks; the advanced units were the hastati, then came the principes; the triarii held the rear.² [2] Outside this, which may be called the regular battle-line, on the [p. 405]right flank and in line with the legions, the consul³ placed the auxiliaries of Eumenes mixed with the Achaean “targeteers,” being about three thousand infantry; outside them he stationed less than three thousand cavalry, eight hundred of whom belonged to Eumenes, all the rest being Roman⁴ cavalry; on the extreme flank he placed the Tralli and Cretans, each contingent amounting to about five hundred men. [3] The left flank did not seem to need such auxiliaries placed there, since the river and its steep banks gave protection on that side; nevertheless, he stationed there four troops of cavalry. [4] This was the whole of the Roman force, with two thousand Macedonians and Thracians who had followed as volunteers; they were left as a guard for the camp. [5] They placed sixteen elephants in reserve behind the triarii, for, in addition to the fact that they seemed unable to face the greater number of the king's elephants —there were fifty-four of them —African elephants cannot resist even an equal number of Indian, whether because the latter are superior in size —for in fact they are far larger —or in fighting spirit.

[6] XL. The king's battle-line was more varied, made up of many races and auxiliary forces differently armed. There were sixteen thousand infantry armed in the Macedonian fashion, who are called phalangitae.⁵ [7] They formed the centre of the line, and their frontage was divided into ten sections; these sections were separated by intervals in which two elephants each were placed; from the front the formation extended thirty-two ranks in depth. [8] This was the main strength of the king's army, and [p. 407]it caused great terror, not only from its general⁶ appearance, but by reason of the elephants, standing out especially conspicuously among the soldiers. They were of great size; head-armour and crests and towers placed upon their backs, and, in addition to the driver, four soldiers riding in each tower, added to their impressiveness. On the right of the phalangitae he stationed fifteen hundred Galatian infantry. [9] To these he added three thousand armoured cavalry —they call them cataphracti.⁷ In addition to these there was a squadron of about a thousand cavalry; they called it the agema;⁸ they were Medes, picked men, and cavalry from many races in the same region mingled with them. [10] Adjoining them a herd of sixteen elephants was posted in reserve. [11] On this side, the flank being advanced a little, was the royal bodyguard; they were called argyraspides⁹ from the character of their equipment; then the Dahae, mounted archers, to the number of twelve hundred; then the light infantry, three thousand in number, about equally divided between Cretans and Tralli; to them two thousand five hundred Mysian archers were added. The extremity of this flank consisted of four thousand mixed Cyrtians, slingers, and Elymaeans, archers. [12] On the left flank, next the phalangitae, were posted fifteen hundred Galatian infantry and two thousand Cappadocians similarly armed —they had been sent to the king by Ariarathes; then twenty-seven hundred auxiliaries mixed from all races, and three thousand armoured cavalry and one thousand other cavalry, [p. 409]the royal squadron, with lighter armour for them¹⁰ selves and their horses, but otherwise with equipment not unlike the rest; they were mostly Syrians mingled with Phrygians and Lydians. [13] In front of this cavalry were scythe-bearing chariots and camels of the breed called dromedaries. These were ridden by Arab archers carrying slender swords four cubits long, that they might be able to reach the enemy from so great a height. Then came another great crowd, corresponding to that on the right flank: first the Tarentini, then twenty-five hundred Galatian cavalry, next a thousand Neocretans and fifteen hundred Carians and Cilicians similarly equipped, and the same number of Tralli and four thousand “targeteers”: [14] these were Pisidians and Pamphylians and Lycians; then auxiliaries of the Cyrtians and Elymaeans equal to those stationed on the right flank, and sixteen elephants a short distance away.¹¹