Pausanias, Description of Greece 2.21.5 - 2.21.6
Medusa's reign over Lake Tritonis
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2.21.5
Not far from the building in the market-place of Argos is a mound of earth, in which they say lies the head of the Gorgon Medusa. I omit the miraculous, but give the rational parts of the story about her. After the death of her father, Phorcus, she reigned over those living around Lake Tritonis, going out hunting and leading the Libyans to battle. On one such occasion, when she was encamped with an army over against the forces of Perseus, who was followed by picked troops from the Peloponnesus, she was assassinated by night. Perseus, admiring her beauty even in death, cut off her head and carried it to show the Greeks.

2.21.6
But Procles, the son of Eucrates, a Carthaginian, thought a different account more plausible than the preceding. It is as follows. Among the incredible monsters to be found in the Libyan desert are wild men and wild women. Procles affirmed that he had seen a man from them who had been brought to Rome. So he guessed that a woman wandered from them, reached Lake Tritonis, and harried the neighbours until Perseus killed her; Athena was supposed to have helped him in this exploit, because the people who live around Lake Tritonis are sacred to her.