Plutarch Sertorius 11

[1] However, at the time of which I speak he set out from Africa on the invitation of the Lusitanians. These he proceeded to organize at once, acting as their general with full powers, and he brought the neighbouring parts of Spain into subjection. Most of the people joined him of their own accord, owing chiefly to his mildness and efficiency; but sometimes he also betook himself to cunning devices of his own for deceiving and charming them. The chief one of these, certainly, was the device of the doe, which was as follows.

[2]
  Spanus, a plebeian who lived in the country, came upon a doe which had newly yeaned and was trying to escape the hunters. The mother he could not overtake, but the fawn—and he was struck with its unusual colour, for it was entirely white—he pursued and caught. And since, as it chanced, Sertorius had taken up his quarters in that region, and gladly received everything in the way of game or produce that was brought him as a gift, and made kindly returns to those who did him such favours, Spanus brought the fawn and gave it to him.

[3] Sertorius accepted it, and at the moment felt only the ordinary pleasure in a gift; but in time, after he had made the animal so tame and gentle that it obeyed his call, accompanied him on his walks, and did not mind the crowds and all the uproar of camp life, he gradually tried to give the doe a religious importance by declaring that she was a gift of Diana, and solemnly alleged that she revealed many hidden things to him, knowing that the Barbarians were naturally an easy prey to superstition.

[4] He also added such devices as these. Whenever he had secret intelligence that the enemy had made an incursion into the territory which he commanded, or were trying to bring a city to revolt from him, he would pretend that the doe had conversed with him in his dreams, bidding him hold his forces in readiness. Again, when he got tidings of some victory won by his generals, he would hide the messenger, and bring forth the doe wearing garlands for the receipt of glad tidings, exhorting his men to be of good cheer and to sacrifice to the gods, assured that they were to learn of some good fortune.