Diodorus Siculus, Historical Library 17.89.1-6 and 17.90.1, 4-7
[Concerning Alexander the Great in India]
Written in the first century B.C.
89.  Many were slain in their flight, but then Alexander, satisfied with his brilliant victory, ordered the trumpets to sound the recall. Of the Indians, there fell in the battle more than twelve thousand, among whom were the two sons of Porus and his best generals and officers.  Above nine thousand men were taken alive, together with eighty elephants. Porus himself was still breathing, and was turned over to the Indians for medical attention.  On the Macedonian side, the losses were two hundred and eighty cavalry and more than seven hundred infantry. The king buried the dead, rewarded those who had distinguished themselves in accordance with their deserts, and sacrificed to Helius who had given him the eastern regions to conquer.  There were mountains not far away where grew thriving firs in quantity, together with no little cedar and pine and an ample supply of other woods suitable for shipbuilding, and Alexander constructed a large number of ships.  He intended to reach the borders of India and to subdue all of its inhabitants, and then to sail downstream to the Ocean.  He founded two cities, one beyond the river where he had crossed and the other on the spot where he had defeated Porus. These were built quickly because there was a plentiful supply of labour. When Porus had recovered, Alexander appointed him, in recognition of his valour, king over the country where he formerly ruled. The Macedonian army rested for thirty days in the midst of a vast plenty of provisions.
90.  Odd phenomena were observed in these mountains. In addition to the wood for shipbuilding, the region contained a large number of snakes remarkable for their size; they reached a length of sixteen cubits….. Sasibisares, the king who had not moved in time to help Porus in the battle, was frightened, and Alexander forced him to accept his orders. Then Alexander resumed his march to the east, crossed the river, and continued on through a region of remarkable fertility.  It possessed strange kinds of trees which reached a height of seventy cubits, were so thick that they could scarcely be embraced by four men, and cast a shadow of three plethra. This country possessed a multitude of snakes, small and variously coloured.  Some of them looked like bronze rods, others had thick, shaggy crests, and their bites brought sudden death. The person bitten suffered fearful pains and was covered with a bloody sweat.  The Macedonians, who were much affected by the bites, slung their hammocks from trees and remained awake most of the night. Later, however, they learned from the natives the use of a medicinal root and were freed from these fears.
Strabo, Ancient Geography 15.1.28
[Concerning Alexander the Great in India]
Written in the first century A.D.
(28) Between the Indus and the Hydaspes is Taxila, a large city, and governed by good laws. The neighbouring country is crowded with inhabitants and very fertile, and here unites with the plains. The people and their king Taxiles received Alexander with kindness, and obtained in return more presents than they had offered to Alexander; so that the Macedonians became jealous, and observed, that it seemed as if Alexander had found none on whom he could confer favours before he passed the Indus. Some writers say that this country is larger than Egypt. Above this country among the mountains is the territory of Abisarus, who, as the ambassadors that came from him reported, kept two serpents, one of 80, and the other, according to Onesicritus, of 140 cubits in length. This writer may as well be called the master fabulist as the master pilot of Alexander. For all those who accompanied Alexander preferred the marvellous to the true, but this writer seems to have surpassed all in his description of prodigies. Some things, however, he relates which are probable and worthy of record, and will not be passed over in silence even by one who does not believe their correctness. Other writers also mention the hunting of serpents in the Emodi mountains, and the keeping and feeding of them in caves.
Quintus Curtius, History of Alexander 4.4.1-5
[Concerning Alexander’s battle with Tyre]
Written in the first century A.D.
At this point Alexander from utter weariness had determined to raise the siege and go to Egypt. For after he had overrun Asia with great speed he was lingering around the walls of a single city, thus losing the opportunity for so many mighty exploits. But he was as much ashamed to withdraw baffled, as to delay, thinking that his reputation also, by which he had overthrown more than by his arms, would be impaired if he should leave Tyre as a witness that he could be defeated. Therefore, in order to leave nothing untried, he ordered more ships to be brought up and the best of his soldiers to be embarked upon them. And it chanced that a sea-monster, of a size never before seen, rising even above the waves with its back, brought its huge body up to the causeway which the Macedonians had built, and striking the surges asunder as it lifted itself, was seen by both sides. Then from the peak of the causeway it again plunged under the sea, and now rising above the surface with a great part of its bulk, now hidden as the waves dashed over it, it disappeared under water not far from the walls of the city. The appearance of the monster gave joy to both sides; the Macedonians interpreted it as showing the direction in which to go on building up the work; the Tyrians thought that Neptune, as an avenger of the usurped sea, had brought the monster against the causeway, and that it would surely soon fall in ruins.
Quintus Curtius, History of Alexander 8.9.14-19; 10.1.11-12
[Concerning Alexander’s exploration and conquest of India]
Certainly the sea by which India is washed does not differ even in colour from other seas. Its name was given it from King Erythrus; for which reason the ignorant believe that its waters are red. The land is rich in flax; hence the greater number of the people wear garments. The bark of the trees is tender and can receive writing just as papyrus does. There are birds which can be taught to imitate the sound of the human voice. The animals are unknown to other nations, except such as are imported from that country. The same land produces rhinoceroses, which are unknown to other peoples. The strength of its elephants is greater than those which men tame in Africa, and their size corresponds to their strength. The rivers which flow sluggishly in a mild and moderate course carry gold. The sea casts upon its shores gems and pearls….
…the sea was full of whales; that these, huge as great ships, floated with the course of the tide, and when frightened off by the blast of the trumpet, from following the ships, plunged under the water with a great roaring of the sea, like so many sunken vessels.
Aulus Gellius, Attic Nights 7.3
Written in the second century A.D.
Tubero in his Histories has recorded that in the first Punic war the consul Atilius Regulus, when encamped at the Bagradas river in Africa, fought a stubborn and fierce battle with a single serpent of extraordinary size, which had its lair in that region; that in a mighty struggle with the entire army the reptile was attacked for a long time with hurling engines and catapults; and that when it was finally killed, its skin, a hundred and twenty feet long, was sent to Rome.