Bava Batra 74a-b
Rab Judah Hindu'a related: Once we were traveling on board a ship when we saw a precious stone that was surrounded by a serpent. A diver descended to bring up the stone. Then the serpent approached to swallow the ship, but a raven came and bit off its head and due to the great size of the serpent the water appeared to turn into blood. A second serpent came, took the stone, placing it on the dead serpent, which brought it back to life. Again the serpent approached the ship, intending to swallow it, but again a bird came and cut off its head. At that point the diver seized the precious stone and threw it into the ship. There were salted birds in the boat, and as soon as the stone was placed on them they came back to life, and taking the stone with them, they flew away with it.
This story is understood as allegory.
The Ritva suggests that the "precious stone" represents wisdom, which can only be attained with great effort. The "serpent" represents the spiritual challenges that impede an individual's progress towards wisdom, and must be removed entirely before wisdom can be achieved. Once a person has achieved wisdom, however, it acts as a life-giving balm, which can revive someone who is spiritually dead.
According to the Maharsha, this is the story of Jewish history. The stone symbolizes Torah, while the serpent symbolizes the Roman government that worked to keep the Jewish people from fulfilling the Torah. Although the Romans tried to destroy the ship - i.e. the Jewish People - another nation - the Moslems - fought against them, and allowed the Jews to live according to their beliefs. He suggests that the "salted fish" were the Torah scholars who suffered at the hands of the Romans, but nevertheless did not despair, and when given the opportunity "flew away" to other lands where they established Jewish communities.