LETO (Latona) was the daughter of Coeus and Phoebe. She was gifted with wonderful beauty, and was tenderly loved by Zeus, but her lot was far from being a happy one, for Hera, being extremely jealous of her, persecuted her with inveterate cruelty, and sent the dreadful serpent Python to terrify and torment her wherever she went.
But Zeus, who had observed with the deepest compassion her weary wanderings and agonized fears, resolved to create for her some place of refuge, however humble, where she might feel herself safe from the venomous attacks of the serpent. He therefore brought her to Delos, a floating island in the Ægean Sea, which he made stationary by attaching it with chains of adamant to the bottom of the sea.
Here she gave birth to her twin-children, Apollo and Artemis (Diana), two of the most beautiful of the immortals. According to some versions of the story of Leto, Zeus transformed her into a quail, in order that she might thus elude the vigilance of Hera, and she is said to have resumed her true form when she arrived at the island of Delos.
From: Berens, E.M. The Myths and Legends of Ancient Greece and Rome. New York: Maynard, Merril, & Co., 1880. Text in the public domain.