In the myths and legends of ancient Greece, the nymphs were commonly known to be spirits of nature - or, on occasion, as minor goddesses in their own right. They were immortal, much like the gods who made their home on Mount Olympus, but they lacked much of the power that the gods could wield.
Nymphs were, in essence, the caretakers of the natural world - and, their presence could be felt in any place where nature was allowed to thrive untouched. Forests and mountains, lakes and streams, even a single solitary tree - any of these could be under the care of one of the many varieties of nymph that were believed to exist.
Nymphs featured often in the stories and legends of ancient Greece. Portrayed as women of almost supernatural beauty they were, naturally, often cast as objects of desire.
The role played by the nymph known as Amalthea (or, Amaltheia) was a fairly small one overall, though. But, it was also one of particular importance. Unlike the majority of her kind, though, Amalthea was not destined to become the object of desire for either god or mortal. Instead, her role was to be that of a caretaker.
In the time before the gods of the Ancient Greek pantheon came to rule at Mount Olympus, the Titan Cronus claimed the throne for himself by overthrowing his father, Uranus (who, along with the goddess, Gaia, was responsible for the creation of the world, according to Greek myth). As the leader of the Titans, Cronus ruled the entirety of the ancient world for many years - but, in that time, he also became aware of a prophecy concerning his own fate. Just as Cronus had overthrown Uranus, this prophecy claimed, so too would Cronus be overthrown by his own child.
Desperate to ensure that this prophecy could never be fulfilled, Cronus set about ensuring that he would never have a child capable of challenging him. In order to achieve this, Cronus began to claim each of his children shortly after they were born, and killing them - devouring them whole. Cronus's wife, the Titan Rhea, was naturally horrified by this, though - and, in her desperation to save at least one of her children, she formed a plan to trick her husband.
Shortly after the birth of her latest child, Rhea knew that it would not be long until her husband came to claim her infant son. So, Rhea found a stone that was roughly the same size and shape as a new-born child, and she wrapped it in blankets - presenting it to Cronus, who promptly swallowed it whole.
The plan worked - and, Cronus left satisfied that the prophecy had been effectively delayed, once more. Meanwhile, the child, who had been named Zeus, was taken away to be raised in secret - carefully hidden from his father.
The infant Zeus was in a cave commonly believed to have been located at Mount Dicte (or, Dikti), on the island of Crete. There, Zeus was placed under the care of Amalthea who, in their years together, came to serve as something of a foster-mother for the young god - seeing to his early education, and feeding him on a mixture of goat's milk and honey.
Here, though, there seems to be some variation in the exact details of the story, depending on its source. Sometimes, Amalthea is believed to have been the name of the goat whose milk provided sustenance for the young Zeus, and his care was largely left to others. At other times, Amalthea was both mother-figure and the goat - possessing the ability to alter her form as required. And, at still others, the nymph and the goat were thought to be entirely separate.
Regardless of the details, though, the role played by Amalthea was largely the same. She was responsible for providing care, and kindness, to the child destined to become the new ruler of Mount Olympus - and, to keep him hidden from his father. As Zeus grew into adulthood, and claimed his position as ruler of Mount Olympus, he sort to reward Amalthea for her devotion, and her protection.
His reward was to place Amalthea among the stars, where she became the constellation Capra - commonly identified with the zodiac sign, Capricorn.