Plutarch Antony 47

[1] After giving this information the man went away, and Antony, who was much troubled by what he now heard, called together his friends and his Mardian guide, who was himself of the same opinion as their visitor. For he knew that even were there no enemy the lack of roads through the plains would involve them in blind and grievous wanderings, and he showed them that the rough road through the mountains had no other annoyance than lack of water for a single day.

[2] Accordingly, Antony took this route and led his army along by night, after ordering his men to carry water with them. The greater part of them, however, had no Vessels, and therefore some actually filled their helmets with water and carried them, while others took it in skins.
  But word was at once brought to the Parthians that Antony was advancing, and contrary to their custom they set out in pursuit while it was yet night. Just as the sun was rising they came up with the rear-guard of the Romans, which was foredone with sleeplessness and toil; for they had accomplished two hundred and forty furlongs in the night. Moreover, they did not expect that the enemy would come upon them so quickly, and were therefore disheartened.

[3] Besides, their contest intensified their thirst; for they had to ward off the enemy and make their way forward at the same time. Those who marched in the van came to a river, the water of which was clear and cold, but had a salty taste and was poisonous. This water, as soon as one drank it, caused pains, accompanied by cramping of the bowels and an inflammation of one’s thirst. Of this too the Mardian had warned them, but none the less the soldiers forced aside those who tried to turn them back, and drank.

[4] Antony went round and begged the men to hold out a little while; for not far ahead, he said, there was another river which was potable, and then the rest of the way was too rough for cavalry, so that the enemy must certainly turn back. At the same time, too, he called his men back from fighting and gave the signal for pitching the tents, that the soldiers might at least enjoy the shade a little.